Communication control method, user terminal, and processor

ABSTRACT

A communication control method is a method for performing offload to transfer a traffic load of a cellular base station to an access point. The communication control method comprises a step of maintaining without releasing the first connection, by a user terminal that have established a first connection with the cellular base station, even when the offload is started after establishing a second connection with the access point; and a determining step of determining, by the user terminal, whether the offload is continued or canceled after the offload is started.

TECHNICAL FIELD

The present invention relates to a communication control method, a userterminal, and a processor, used in cellular communication system allowedto cooperate with a wireless LAN system (a WLAN system).

BACKGROUND ART

In recent years, a user terminal (so-called dual terminal) comprising acellular communication unit and a wireless LAN communication unit isbecoming widely used. Further, the number of wireless LAN access points(hereinafter called “access points”) managed by an operator of acellular communication system increases.

Therefore, in 3GPP (3rd Generation Partnership Project) which is aproject aiming to standardize a cellular communication system, it isexpected to consider a technology capable of enhancing cooperationbetween a cellular communication system and a wireless LAN system (seeNon Patent Document 1).

One purpose of such technology is that balance of load level in acellular base station and an access point is taken by improving usagerate of access point.

For example, it is possible to transfer (offload) traffic load of acellular base station to an access point by switch such that traffictransmitted and received between the cellular base station and a userterminal is transmitted and received between the access point and theuser terminal.

PRIOR ART DOCUMENT Non-Patent Document

Non-Patent Document 1: 3GPP contribution “RP-1201455”

SUMMARY OF THE INVENTION

By the way, the user terminal generally releases a connection with acellular base station in a case where a user terminal establishes aconnection with an access point. Thus, the user terminal becomes an idlestate of the cellular communication during performing the above offload.

However, an inefficient operation (so-called ping-pong phenomenon) thatthe connection between the user terminal and the cellular base stationis anew established may occur in such cases where communication statusbetween the user terminal and the access point deteriorates afterestablishing the connection between the user terminal and the accesspoint.

Therefore, an object of the present invention is to effectively controlthe offload to transfer the traffic load of a cellular base station toan access point.

A communication control method according to an embodiment is a methodfor performing offload to transfer a traffic load of a cellular basestation to an access point. The communication control method comprises astep of maintaining without releasing the first connection, by a userterminal that have established a first connection with the cellular basestation, even when the offload is started after establishing a secondconnection with the access point; and a determining step of determining,by the user terminal, whether the offload is continued or canceled afterthe offload is started.

A user terminal according to an embodiment comprises: a controllerconfigured to establish a second connection with an access point whichis included in a wireless local area network (WLAN) and start offload totransfer a traffic of a mobile communication network to the WLAN, whenthe user terminal has established the first connection with a basestation which is included in the mobile communication network. Thecontroller maintains the first connection even after the offload isstarted. The controller determines whether to continue the offload ornot.

A processor according to a processor for controlling a user terminal.The processor comprises: a step of establishing a second connection withan access point which is included in a wireless local area network(WLAN) and starting offload to transfer a traffic of a mobilecommunication network to the WLAN, when the user terminal hasestablished the first connection with a base station which is includedin the mobile communication network; a step of maintaining the firstconnection even after the offload is started, and a step of determiningwhether to continue the offload or not.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system configuration diagram according to a first embodimentand a second embodiment.

FIG. 2 is a block diagram of an UE (an user terminal) according to thefirst embodiment and the second embodiment.

FIG. 3 is a block diagram of an eNB (a cellular base station) accordingto the first embodiment and the second embodiment.

FIG. 4 is a block diagram of an AP (an access point) according to thefirst embodiment and the second embodiment.

FIG. 5 is a protocol stack diagram of a radio interface in an LTEsystem.

FIG. 6 is a configuration diagram of a radio frame used in the LTEsystem.

FIG. 7 is a diagram for describing operation environment according tothe first embodiment and the second embodiment.

FIG. 8 is a sequence diagram of an operation pattern 1 according to thefirst embodiment.

FIG. 9 is a sequence diagram of an operation pattern 2 according to thefirst embodiment.

FIG. 10 is a sequence diagram of an operation pattern 2 according to thesecond embodiment.

FIG. 11 is a sequence diagram of an operation pattern 3 according to thesecond embodiment.

FIG. 12 is a sequence diagram of an operation pattern 4 according to thesecond embodiment.

FIG. 13 is a diagram for describing an operation environment accordingto a third embodiment and a fourth embodiment.

FIG. 14 is an operation flow diagram of a UE 100 according to the thirdembodiment.

FIG. 15 is a sequence diagram according to a modification of the thirdembodiment and a modification of the fourth embodiment.

FIG. 16 is an operation flow diagram of the UE 100 according to thefourth embodiment.

FIG. 17 is a system configuration diagram according to a fifthembodiment.

FIG. 18 is a diagram for describing an operation environment accordingto the fifth embodiment.

FIG. 19 is a sequence diagram of an offload operation according to thefifth embodiment.

FIG. 20 is a system configuration diagram according to a sixthembodiment and a seventh embodiment.

FIG. 21 is a block diagram of a HeNB according to the sixth embodimentand the seventh embodiment.

FIG. 22 is a diagram showing a positional relation among the UE 100, aneNB 200, a HeNB 400, and an AP 300 according to the sixth embodiment.

FIG. 23 is a sequence diagram for describing an operation according tothe sixth embodiment.

FIG. 24 is a sequence diagram for describing an operation according tothe sixth embodiment.

FIG. 25 is a diagram showing a positional relation among the UE 100, theeNB 200, the HeNB 400, and the AP 300 according to the seventhembodiment.

FIG. 26 is a sequence diagram for describing an operation according tothe seventh embodiment.

DESCRIPTION OF THE EMBODIMENT

[Overview of Embodiment]

A communication control method according to the first embodiment and thesecond embodiment is a method for performing offload to transfer atraffic load of a cellular base station to an access point. Thecommunication control method comprises a step of maintaining withoutreleasing the first connection, by a user terminal that have establisheda first connection with the cellular base station, even when the offloadis started after establishing a second connection with the access point;and a determining step of determining, by the user terminal, whether theoffload is continued or canceled after the offload is started.

In the first embodiment and the second embodiment, in the determiningstep, the user terminal carries out the determination on the basis of acommunication status with the access point.

In the operation pattern 1 according to the first embodiment, thecommunication control method further comprises: a step of receiving fromthe cellular base station, before the first connection is released, bythe user terminal, configuration information for configuration of anoperation of the user terminal after the first connection is released.

In the operation pattern 1 according to the first embodiment, thecommunication control method further comprises: a step of transmitting,by the user terminal, a notification indicating that the offload iscontinued, to the cellular base station, when it is determined in thedetermining step that the offload is continued; and a step of releasing,by the user terminal, the first connection after the notification istransmitted.

In the operation pattern 1 according to the first embodiment, thecommunication control method further comprises: a step of canceling theoffload and discarding the configuration information, by the userterminal, when it is determined in the determining step that the offloadis canceled.

In the operation pattern 2 according to the first embodiment, thecommunication control method further comprises a step of transmitting,to the cellular base station, by the user terminal, a transmission stoprequest for requesting to stop transmitting a release instruction of thefirst connection, before the offload is started.

In the operation pattern 2 according to the first embodiment, thecommunication control method further comprises: a step of transmitting,to the cellular base station, by the user terminal, a transmissionrequest to request to transmit the release instruction when it isdetermined in the determining step that the offload is continued; and astep of receiving, by the user terminal, the release instruction fromthe cellular base station. The release instruction includesconfiguration information for configuration of an operation of the userterminal, after the first connection is released.

In the first embodiment and the second embodiment, the user terminalcomprises a terminal-side timer that regulates a connection maintainingperiod during which the first connection should be maintained after theoffload is started. The communication control method further comprises:a step of activating, by the user terminal, the terminal-side timer whenthe offload is started; and a maintaining step of maintaining, by theuser terminal, the first connection until the terminal-side timerexpires.

In the operation pattern 1 according to the second embodiment, thecellular base station comprises a base station-side timer that regulatesa connection maintaining period during which the first connection shouldbe maintained after transmission and reception of traffic with the userterminal is stopped. The connection maintaining period set to theterminal-side timer is equal to or shorter than the connectionmaintaining period set to the base station-side timer.

In the operation pattern 2 according to the second embodiment, thecellular base station comprises a base station-side timer that regulatesa connection maintaining period during which the first connection shouldbe maintained after transmission and reception of traffic with the userterminal is stopped. In the maintaining step, the user terminaltransmits and receives the traffic with the access point and transmitsand receives the traffic with the cellular base station for stopping thebase station-side timer.

In the operation pattern 3 according to the second embodiment, thecellular base station comprises a base station-side timer that regulatesa connection maintaining period during which the first connection shouldbe maintained after transmission and reception of traffic with the userterminal is stopped. The communication control method further comprisesa step of inquiring the user terminal from the cellular base station ofwhether it is possible to release the first connection in a case wherethe release request for the first connection is not received from theuser terminal when the base station-side timer expires in the cellularbase station.

In the operation pattern 4 according to the second embodiment, thecellular base station comprises a base station-side timer that regulatesa connection maintaining period during which the first connection shouldbe maintained after transmission and reception of traffic with the userterminal is stopped. The communication control method further comprisesa control step of controlling, by the cellular base station, the basestation-side timer in order to prevent the base station-side timer fromexpiring before the terminal-side timer expires.

In the operation pattern 4-1 according to the second embodiment, thebase station-side timer includes a first base station-side timer usedfor a purpose of other than the offload and a second base station-sidetimer used for a purpose of the offload. The connection maintainingperiod set to the second base station-side timer is longer than theconnection maintaining period set to the first base station-side timer.In the control step, the cellular base station selects the second basestation-side timer and then activates the second base station-sidetimer, in response to a start of the offload.

In the operation pattern 4-2 according to the second embodiment, thecommunication control method further comprises a step of notifying, bythe cellular base station, the user terminal of the connectionmaintaining period that should be set to the terminal-side timer. In thecontrol step, the cellular base station sets the connection maintainingperiod equal to or longer than the connection maintaining periodnotified to the user terminal, to the base station-side timer.

In the operation pattern 4-3 according to the second embodiment, in thecontrol step, the cellular base station cancels the activation of thebase station-side timer in response to the start of the offload.

A user terminal according to the third embodiment comprises a cellularcommunication unit and a WLAN communication unit. The user terminalcomprises: a controller configured to measure a movement speed of theuser terminal when the WLAN communication unit is in an on state. Thecontroller restricts a start of connection by the WLAN communicationunit with an access point when detecting a rapid decrease in themovement speed.

In the third embodiment, the controller cancels the restriction of thestart of the connection when detecting a rapid increase in the movementspeed after detecting the rapid decrease in the movement speed.

In the modification of the third embodiment, it further comprises: astorage configured to store a list of the access points that should besubject to the connection restriction. The controller restricts a startof connection with the access point included in the list.

In the third embodiment, the cellular communication unit receives thelist from a cellular base station. The storage stores the list receivedfrom the cellular base station.

A user terminal according to the fourth embodiment comprises a cellularcommunication unit and a WLAN communication unit. The user terminalcomprises: a controller configured to measure a reception level from anaccess point when the WLAN communication unit is in an on state. Thecontroller restricts a start of connection by the WLAN communicationunit with the access point when detecting a rapid increase in thereception level.

In the fourth embodiment, the controller cancels the restriction of thestart of the connection when detecting a rapid decrease in the receptionlevel after detecting the rapid increase in the reception level.

In the modification of the fourth embodiment, it further comprises: astorage configured to store a list of the access points that should besubject to the connection restriction. The controller restricts thestart of connection with the access point included in the list.

In the modification of the fourth embodiment, the cellular communicationunit receives the list from a cellular base station. The storage storesthe list received from the cellular base station.

A user terminal according to the fifth embodiment comprises: a cellularcommunication unit configured to transmit and receive a cellular radiosignal with a cellular base station; a WLAN communication unitconfigured to transmit and receive a WLAN radio signal with an accesspoint; and a controller configured to switch the WLAN communication unitto an on state, when the WLAN communication unit is in an off state andwhen the cellular communication unit receives, from the cellular basestation, a WLAN on request for switching the WLAN communication unit tothe on state. The WLAN on request includes scan control information forcontrolling a WLAN scan that is an operation in which reception of theWLAN radio signal is attempted by the WLAN communication unit for eachWLAN channel. The controller controls the WLAN scan in accordance withthe scan control information included in the WLAN on request afterswitching the WLAN communication unit to the on state.

In the fifth embodiment, the controller notifies, before receiving theWLAN on request, the cellular base station of at least one ofinformation indicating a WLAN communication capability of the userterminal and information indicating that the WLAN communication unit isin an off state.

In the fifth embodiment, the scan control information includes at leastone of channel information for designating a WLAN channel subject to theWLAN scan or a WLAN channel not subject to the WLAN scan, and frequencyband information for designating a WLAN frequency band subject to theWLAN scan or a WLAN frequency band not subject to the WLAN scan.

In the fifth embodiment, the scan control information includes priorityinformation for designating a WLAN channel or a WLAN frequency bandwhere reception of the WLAN radio signal should be preferentiallyattempted in the WLAN scan.

In the fifth embodiment, the scan control information includes at leastone of period information for designating a period during which the WLANscan should be continued, and timing information for designating atiming at which the WLAN scan should be performed.

In the fifth embodiment, the user terminal further comprises: a GNSSreceiver configured to receive a GNSS (Global Navigation SatelliteSystem) signal. The controller notifies the cellular base station ofinformation on a reception level of the GNSS signal prior to receptionof the WLAN on request.

In the fifth embodiment, the controller ignores the WLAN on request whenthe WLAN communication unit is in an on state and when the cellularcommunication unit receives, from the cellular base station, the WLAN onrequest.

A communication control method according to the sixth embodiment is acommunication control method for allowing a cellular communicationsystem to cooperate with a wireless LAN system, and comprises: adetermination step of determining whether or not a connection between awireless LAN access point directly connected to a small cell basestation and a user terminal connected to the wireless LAN access pointbecomes difficult; a connection step of connecting, by the userterminal, to a cell managed by another base station, when it isdetermined that the connection between the user terminal and thewireless LAN access point becomes difficult; and a transfer step oftransferring, by the wireless LAN access point, user data on the userterminal owned by the wireless LAN access point by way of the small cellbase station to the another base station when it is determined that theconnection between the user terminal and the wireless LAN access pointbecomes difficult.

The communication control method according to the sixth embodimentfurther comprises: a request step of making, by the user terminal, arequest to transfer the user data to the another base station when it isdetermined in the determination step that the connection between theuser terminal and the wireless LAN access point becomes difficult,wherein in the transfer step, the wireless LAN access point transfers,resulting from the request in the request step, the user data to theanother base station by way of the small cell base station.

In the communication control method according to the sixth embodiment,in the determination step, the user terminal determines that theconnection with the wireless LAN access point becomes difficult, even ifa signal intensity received from the wireless LAN access point is equalto or more than a predetermined value that is a value by which it ispossible to ensure communication quality, when the wireless LAN accesspoint is of collocated type in which the wireless LAN access point isdisposed at the same place as the small cell base station, and a signalintensity received from the small cell base station is less than apredetermined value.

The communication control method according to the sixth embodimentfurther comprises: a first transfer request step of requesting, whenreceiving the request in the request step, by the another base station,the small cell base station to transfer the user data to the anotherbase station from the wireless LAN access point by way of the small cellbase station; and a second transfer request step of requesting, whenreceiving the request in the first transfer request step, by the smallcell base station, the wireless LAN access point to transfer the userdata to the small cell base station, wherein in the transfer step, whenreceiving the request in the second transfer request step, the wirelessLAN access point receives transfers the user data to the another basestation by way of the small cell base station.

In the communication control method according to the sixth embodiment,in the transfer step, when the small cell base station is a home basestation that manages a specific cell to which only a specific userterminal having an access right is connectable, and even when the userterminal is not the specific user terminal, the small cell base stationtransfers the user data transferred from the wireless LAN access pointto the another base station.

The communication control method according to the sixth embodimentfurther comprises: a negative acknowledgment step of sending a negativeacknowledgment, by the another base station, to the request in therequest step, when it is not possible to satisfy the request in therequest step; and a re-request step of re-making, by the user terminal,a request in the request step, when receiving the negativeacknowledgment.

In the communication control method according to the sixth embodiment,in the re-request step, the user terminal repeats the request in therequest step until the number of times that the negative acknowledgmentis received reaches a predetermined value.

In the communication control method according to another embodiment, inthe determination step, the wireless LAN access point determines thatthe connection between the user terminal and the wireless LAN accesspoint becomes difficult, when a signal intensity received from the userterminal is less than a predetermined value.

A communication control method according to the seventh embodiment is acommunication control method for allowing a cellular communicationsystem to cooperate with a wireless LAN system, and comprises: adetermination step of determining whether or not a connection between awireless LAN access point directly connected to a small cell basestation and a user terminal connected to the wireless LAN access pointbecomes difficult; a connection step of connecting, by the userterminal, to a small cell managed by the small cell base station, whenit is determined that the connection between the user terminal and thewireless LAN access point becomes difficult; and a transfer step oftransferring, by the wireless LAN access point, user data on the userterminal owned by the wireless LAN access point to the small cell basestation when it is determined that the connection between the userterminal and the wireless LAN access point becomes difficult.

The communication control method according to the seventh embodimentfurther comprises: a request step of requesting, by the user terminal,to transfer the user data to the small base station when it isdetermined in the determination step that the connection between theuser terminal and the wireless LAN access point becomes difficult,wherein in the transfer step, the wireless LAN access point transfers,on the basis of the request in the request step, the user data to thesmall cell base station.

In the communication control method according to the seventh embodiment,in the determination step, the user terminal determines that theconnection with the wireless LAN access point becomes difficult, whenthe wireless LAN access point is of collocated type in which thewireless LAN access point is disposed at the same place as the smallcell base station, and before a signal intensity received from the smallcell base station is less than a predetermined value that is a value bywhich it is possible to ensure a communication quality, when the signalintensity received from the wireless LAN access point is less than apredetermined value.

In the communication control method according to the seventh embodiment,in the determination step, the wireless LAN access point determines thatthe connection between the user terminal and the wireless LAN accesspoint becomes difficult, when a signal intensity received from the userterminal is less than a predetermined value.

The communication control method according to the seventh embodiment,further comprises: a handover request step of making, to another basestation adjacent to a small cell base station, a handover requestrequesting the user data transferred from the wireless LAN access pointand a handover to a cell immediately after the small cell and the userterminal are connected, when the small cell base station is a home basestation configured to manage a specific cell to which only a specificuser terminal having an access right is connectable and when the userterminal is not the specific user terminal.

Next, a first embodiment to a seventh embodiment will be described. Itis noted that in each of the embodiments, a description proceeds with afocus on a difference from another embodiment, and a like part will notbe described where appropriate.

[First Embodiment]

Hereinafter, with reference to the drawing, an embodiment will bedescribed in which a cellular communication system (an LTE system)configured in compliance with the 3GPP standards is allowed to cooperatewith a wireless LAN (WLAN) system.

(System Configuration)

FIG. 1 is a system configuration diagram according to the firstembodiment. As shown in FIG. 1, the cellular communication systemincludes a plurality of UEs (User Equipments) 100, E-UTRAN (EvolvedUniversal Terrestrial Radio Access Network) 10, and EPC (Evolved PacketCore) 20. The E-UTRAN 10 corresponds to a radio access network. The EPC20 corresponds to a core network.

The UE 100 is a mobile radio communication device and performs radiocommunication with a cell with which a connection is established. The UE100 corresponds to the user terminal. The UE 100 is a terminal (dualterminal) that supports both cellular communication scheme and WLANcommunication scheme.

The E-UTRAN 10 includes a plurality of eNBs 200 (evolved Node-Bs). TheeNB 200 corresponds to a cellular base station. The eNB 200 manages oneor a plurality of cells and performs radio communication with the UE 100which establishes a connection with the cell of the eNB 200. It is notedthat the “cell” is used as a term indicating a minimum unit of a radiocommunication area, and is also used as a term indicating a function ofperforming radio communication with the UE 100. Further, the eNB 200,for instance, has a radio resource management (RRM) function, a routingfunction of user data, and a measurement control function for mobilitycontrol and scheduling.

The eNBs 200 are connected mutually via an X2 interface. Further, theeNB 200 is connected to MME/S-GW 500 included in the EPC 20 via an Siinterface.

The EPC 20 includes a plurality of MMEs (Mobility ManagementEntities)/S-GWs (Serving-Gateways) 500. The MME is a network node forperforming various mobility controls, etc., for the UE 100 andcorresponds to a controller. The S-GW is a network node that performstransfer control of user data and corresponds to a mobile switchingcenter.

The WLAN system includes WLAN access point (hereinafter, called “AP”)300. The WLAN system is configured to be in compliance with some IEEE802.11 standards, for example. The AP 300 communicates with the UE 100in a frequency band (WLAN frequency band) different from a cellularfrequency band. The AP 300 is connected to the EPC 20 via a router, etc.

It is noted that there may be one WLAN frequency band; there may be aplurality of WLAN frequency bands (for example, 2.4 GHz band and 5 GHzband). A plurality of WLAN channels may be included in one WLANfrequency band.

Further, it is not limited to the case where the eNB 200 and the AP 300are separately disposed. The eNB 200 and the AP 300 may be disposed inthe same place (Collocated). The eNB 200 and the AP 300 are directlyconnected by arbitrary interface of an operator as one embodiment ofCollocated.

Subsequently, a configuration of the UE 100, the eNB 200, and the AP 300will be described.

FIG. 2 is a block diagram of the UE 100. As shown in FIG. 2, the UE 100includes: antennas 101 and 102; a cellular communication unit (acellular transceiver) 111; a WLAN communication unit (a WLANtransceiver) 112; a user interface 120; a GNSS (Global NavigationSatellite System) receiver 130; a battery 140; a memory 150; and aprocessor 160. The memory 150 and the processor 160 configure acontroller. Alternatively, the memory 150 configures a storage and theprocessor 160 configures a controller. The UE 100 may not have the GNSSreceiver 130. Furthermore, the memory 150 may be integrally formed withthe processor 160, and this set (that is, a chipset) may be called aprocessor 160′ configuring a controller (and a storage).

The antenna 101 and the cellular communication unit 111 are used fortransmitting and receiving a cellular radio signal. The cellularcommunication unit 111 converts a baseband signal output from theprocessor 160 into the cellular radio signal, and transmits the samefrom the antenna 101. Further, the cellular communication unit 111converts the cellular radio signal received by the antenna 101 into thebaseband signal, and outputs the same to the processor 160.

The antenna 102 and the WLAN communication unit 112 are used fortransmitting and receiving a WLAN radio signal. The WLAN communicationunit 112 converts the baseband signal output from the processor 160 intoa WLAN radio signal, and transmits the same from the antenna 102.Further, the WLAN communication unit 112 converts the WLAN radio signalreceived by the antenna 102 into a baseband signal, and outputs the sameto the processor 160.

The user interface 120 is an interface with a user carrying the UE 100,and includes, for example, a display, a microphone, a speaker, andvarious buttons. Upon receipt of the input from a user, the userinterface 120 outputs a signal indicating a content of the input to theprocessor 160. The GNSS receiver 130 receives a GNSS signal in order toobtain location information indicating a geographical location of the UE100, and outputs the received signal to the processor 160. The battery140 accumulates a power to be supplied to each block of the UE 100.

The memory 150 stores a program to be executed by the processor 160 andinformation to be used for a process by the processor 160. The processor160 includes the baseband processor that performs modulation anddemodulation, and encoding and decoding on the baseband signal and a CPUthat performs various processes by executing the program stored in thememory 150. The processor 160 may further include a codec that performsencoding and decoding on sound and video signals. The processor 160executes various processes and various communication protocols describedlater.

FIG. 3 is a block diagram of the eNB 200. As shown in FIG. 3, the eNB200 includes an antenna 201, a cellular communication unit (a cellulartransceiver) 210, a network interface 220, a memory 230, and a processor240. The memory 230 and the processor 240 configure a controller.Furthermore, the memory 230 may be integrally formed with the processor240, and this set (that is, a chipset) may be called a processorconfiguring a controller.

The antenna 201 and the cellular communication unit 210 are used fortransmitting and receiving a cellular radio signal. The cellularcommunication unit 210 converts the baseband signal output from theprocessor 240 into the cellular radio signal, and transmits the samefrom the antenna 201. Furthermore, the cellular communication unit 210converts the cellular radio signal received by the antenna 201 into thebaseband signal, and outputs the same to the processor 240.

The network interface 220 is connected to the neighboring eNB 200 via anX2 interface and is connected to the MME/S-GW 500 via the Si interface.Further, the network interface 220 is used for communication with the AP300 via the EPC 20.

The memory 230 stores a program to be executed by the processor 240 andinformation to be used for a process by the processor 240. The processor240 includes the baseband processor that performs modulation anddemodulation, encoding and decoding and the like on the baseband signaland a CPU that performs various processes by executing the programstored in the memory 230. The processor 240 implements various processesand various communication protocols described later.

FIG. 4 is a block diagram of the AP 300. As shown in FIG. 4, the AP 300includes an antenna 301, a WLAN communication unit (a WLAN transceiver)311, a network interface 320, a memory 330, and a processor 340. Thememory 330 and the processor 340 configure a controller. Furthermore,the memory 330 may be integrally formed with the processor 340, and thisset (that is, a chipset) may be called a processor configuring acontroller.

The antenna 301 and the WLAN communication unit 311 are used fortransmitting and receiving the WLAN radio signal. The WLAN communicationunit 311 converts the baseband signal output from the processor 340 intothe WLAN radio signal and transmits the same from the antenna 301.Further, the WLAN communication unit 311 converts the WLAN radio signalreceived by the antenna 301 into the baseband signal and outputs thesame to the processor 340.

The network interface 320 is connected to the EPC 20 via a router, etc.Further, the network interface 320 is used for communication with theeNB 200 via the EPC 20.

The memory 330 stores a program executed by the processor 340 andinformation used for a process by the processor 340. The processor 340includes the baseband processor that performs modulation anddemodulation, and encoding and decoding on the baseband signal and a CPUthat performs various processes by executing the program stored in thememory 330.

FIG. 5 is a protocol stack diagram of a radio interface in the cellularcommunication system. As shown in FIG. 5, the radio interface protocolis classified into a layer 1 to a layer 3 of an OSI reference model,wherein the layer 1 is a physical (PHY) layer. The layer 2 includes aMAC (Media Access Control) layer, an RLC (Radio Link Control) layer, anda PDCP (Packet Data Convergence Protocol) layer. The layer 3 includes anRRC (Radio Resource Control) layer.

The PHY layer performs encoding and decoding, modulation anddemodulation, antenna mapping and demapping, and resource mapping anddemapping. Between the PHY layer of the UE 100 and the PHY layer of theeNB 200, data is transmitted via the physical channel.

The MAC layer performs priority control of data, and a retransmissionprocess and the like by hybrid ARQ (HARQ). Between the MAC layer of theUE 100 and the MAC layer of the eNB 200, data is transmitted via atransport channel. The MAC layer of the eNB 200 includes a scheduler forselecting a transport format (a transport block size, a modulation andcoding scheme and the like) of an uplink and a downlink, and an assignedresource block.

The RLC layer transmits data to an RLC layer of a reception side byusing the functions of the MAC layer and the PHY layer. Between the RLClayer of the UE 100 and the RLC layer of the eNB 200, data istransmitted via a logical channel.

The PDCP layer performs header compression and decompression, andencryption and decryption.

The RRC layer is defined only in a control plane. Between the RRC layerof the UE 100 and the RRC layer of the eNB 200, a control message (anRRC message) for various types of setting is transmitted. The RRC layercontrols the logical channel, the transport channel, and the physicalchannel in response to establishment, re-establishment, and release of aradio bearer. When there is a connection (RRC connection) between theRRC of the UE 100 and the RRC of the eNB 200, the UE 100 is in aconnected state (RRC connected state); otherwise, the UE 100 is in anidle state (RRC idle state).

A NAS (Non-Access Stratum) layer positioned above the RRC layer performssession management or mobility management, for example.

FIG. 6 is a configuration diagram of a radio frame used in the LTEsystem. In the LTE system, OFDMA (Orthogonal Frequency DivisionMultiplexing Access) is applied to a downlink, and SC-FDMA (SingleCarrier Frequency Division Multiple Access) is applied to an uplink,respectively.

As shown in FIG. 6, the radio frame is configured by 10 subframesarranged in a time direction, wherein each subframe is configured by twoslots arranged in the time direction. Each subframe has a length of 1 msand each slot has a length of 0.5 ms. Each subframe includes a pluralityof resource blocks (RBs) in a frequency direction, and a plurality ofsymbols in the time direction. The resource block includes a pluralityof subcarriers in the frequency direction.

Among radio resources assigned to the UE 100, a frequency resource canbe designated by a resource block and a time resource can be designatedby a subframe (or slot).

In the downlink, an interval of several symbols at the head of eachsubframe is a control region mainly used as a physical downlink controlchannel (PDCCH). Furthermore, the remaining interval of each subframe isa region that can be mainly used as a physical downlink shared channel(PDSCH). Furthermore, in the downlink, reference signals such ascell-specific reference signals are distributed and arranged in eachsubframe.

In the uplink, both ends, in the frequency direction, of each subframeare control regions mainly used as a physical uplink control channel(PUCCH). Furthermore, the center portion, in the frequency direction, ofeach subframe is a region that can be mainly used as a physical uplinkshared channel (PUSCH).

(Operation According to First Embodiment)

Next, an operation according to the first embodiment will be described.

(1) Operation Environment

FIG. 7 is a diagram for describing operation environment according tothe first embodiment. As shown in FIG. 7, the AP 300 is provided incoverage of the eNB 200. The AP 400 is an AP (an Operator controlled AP)managed by an operator.

Further, a plurality of UEs 100 is located within the coverage of theeNB 200 and within coverage of the AP300. The UE 100 establishes aconnection with the eNB 200 and performs cellular communication with theeNB 200. Specifically, the UE 100 transmits and receives cellular radiosignal including traffic (user data) with the eNB 200. Alternatively,some UEs 100 may not establish the connection with the eNB 200.

A load level of the eNB 200 becomes high when the eNB 200 establishesconnections with a large number of UEs 100. The load level meanscongestion degree of the eNB 200 such as traffic load of the eNB 200 orradio resource usage rate of the eNB 200.

The traffic load of the eNB 200 can be transferred (offloaded) to theAP300 by switching so that traffic transmitted and received between theeNB 200 and the UE 100 is transmitted and received between the AP 300and the UE 100.

However, the UE 100 becomes the idle state of cellular communicationduring performing the offload because of releasing the connection withthe eNB 200 when the UE 100 generally establishes the connection withthe AP300.

Thus, an inefficient operation (so-called ping-pong phenomenon) that theconnection between the UE 100 and the eNB 200 is anew established mayoccur in such a case that communication status between the UE 100 andthe AP 300 deteriorates after establishing the connection between the UE100 and the AP 300.

Hereinafter, an operation according to the first embodiment forresolving this defect will be described

(2) Operation Pattern 1 According to the First Embodiment

FIG. 8 is a sequence diagram of an operation pattern 1 according to thefirst embodiment. In an initial state of the present sequence, the UE100is in a state in which the UE100 has established a RRC connection (afirst connection) with the eNB 200.

As shown in FIG. 8, in step S101, when the UE 100 decides on starting ofthe offload, the UE 100 transmits an offload notification to that effectto the eNB 200.

In step S102, the eNB 200 transmits an acknowledgment (an Ack) to the UE100 in response to a receipt of the offload notification from the UE100. The eNB 200 transmits configuration information (hereinafter called“idle time configuration information”) for configuration of an operation(that is, an operation in the idle state) of the UE 100 after the RRCconnection is released, to the UE 100 along with the Ack. When the UE100 receives the idle time configuration information along with the Ack,the UE 100 stores the received idle time configuration information. Theidle time configuration information is information similar toinformation included in a RRC release message (a RRC Connection Release)and information (such as freqPriorityList, idleModeMobilityControlInfo)for providing priority of cell reselection (Refer to 3GPP technicalspecification “TS 36.300”).

In step S103, the UE 100 establishes a connection (a second connection)with the AP 300 in response to a receipt of the Ack from the eNB 200,and then the offload is started. Specifically, the UE 100 switches thetraffic transmitted and received with the eNB 200 so as to betransmitted and received with the AP 300.

The UE 100 and the eNB 200 maintain without releasing the RRC connectioneven when the offload is started. Thus, the UE 100 maintains theconnection state of the cellular communication without transition to theidle state of the cellular communication even when the offload isstarted.

In step S104, the UE 100 activates a timer for measuring a predeterminedtime.

When the timer expires in step S105, the UE 100 determines whether theoffload is continued or not in step S106. In other words, the UE 100determines whether the UE 100 switches the traffic transmitted andreceived with the AP 300 so as to be transmitted and received with theeNB 200. The UE 100 carries out the determination on the basis of acommunication status with the AP 300. The communication status with theAP 300 is radio link status between the UE 100 and the AP 300 and/ornetwork status relevant to the AP 300. The radio link status between theUE100 and the AP 300 is signal intensity of beacon signal, radio linkstability degree and the like. The network status relevant to the AP 300is load level of the AP 300 and the like. For example, when thecommunication status between the UE 100 and the AP 300 is good, the UE100 determines that the offload is continued, and otherwise the UE 100determines that the offload is cancelled.

When it is determined that the offload is cancelled (in step S106: No),the UE 100 cancels the offload in step S107. In other words, the UE 100switches the traffic transmitted and received with the AP 300 so as tobe transmitted and received with the eNB 200. Further, in step S108, theUE 100 discards the idle time configuration information stored in stepS102. Also, the UE 100 may release the connection of the AP 300.

On the other hand, when it is determined that the offload is continued(in step S106: Yes), the UE 100 transmits notification indicating thatthe offload is continued to the eNB 200 in step S109. As a result, theUE 100 and the eNB 200 release the RRC connection. Further, the UE 100transits from the connection state of the cellular communication to theidle state.

In step S110, the UE 100 applies the idle time configuration informationstored in step S102. Then, in step S111, the UE 100 performs anoperation in the idle state on the basis of the idle time configurationinformation.

(3) Operation Pattern 2 According to the First Embodiment

FIG. 9 is a sequence diagram of an operation pattern 2 according to thefirst embodiment. In an initial state of the present sequence, the UE100 is in a state in which the UE 100 has established the RRC connection(the first connection) with the eNB 200.

As shown in FIG. 9, in step S201, when the UE 100 decides on starting ofthe offload, the UE 100 transmits an offload notification to that effectto the eNB 200. The UE 100 transmits transmission stop request forrequesting to stop transmitting a release instruction (a RRC releasemessage) of the RRC connection along with the offload notification. TheeNB 200 sets a stopping transmitting the RRC release message to the UE100 in the response to a receipt of the transmission stop request.

In step S202, the eNB 200 transmits an acknowledgment (an Ack) to the UE100 in the response to a receipt of the offload notification from the UE100.

In step S203, the UE 100 establishes the connection (the secondconnection) with the AP 300 on the basis of the Ack from the eNB 200,and then the offload is started. Specifically, the UE 100 switches thetraffic transmitted and received with the eNB 200 so as to betransmitted and received with the AP 300.

The UE 100 and the eNB 200 maintain without releasing the RRC connectioneven when the offload is started. Thus, the UE 100 maintains theconnection state of the cellular communication without transition to theidle state of the cellular communication even when the offload isstarted.

In step S204, the UE 100 activates a timer for measuring a predeterminedtime.

In step S205, the UE 100 determines whether the offload is continued ornot. A method of determination is the same as that of the operationpattern 1.

When it is determined that the offload is cancelled (in step S205: No),the UE 100 cancels the offload in step S206. In other words, the UE 100switches the traffic transmitted and received with the AP 300 so as tobe transmitted and received with the eNB 200. Also, the UE 100 mayrelease the connection of the AP 300.

On the other hand, when it is determined that the offload is continued(in step S205: Yes) and when the timer expires (in step S207), the UE100 transmits a transmission request to request to transmit the RRCrelease message to the eNB 200 in step S208.

In step S209, the eNB 200 transmits the RRC release message to the UE100 in a response to a receipt of the transmission request of the RRCrelease message. The RRC release message includes the idle timeconfiguration information for configuration of an operation of the UE100 after the RRC connection is released. As a result, the UE 100 andthe eNB 200 release the RRC connection. Further, the UE 100 transitsfrom the connection state of the cellular communication to the idlestate. Then in step S210, the UE 100 performs an operation in the idlestate on the basis of the idle time configuration information.

(Conclusion of the First Embodiment)

In the first embodiment, the UE 100 that have established the RRCconnection with the eNB 200 maintains without releasing the RRCconnection even when the offload is started after establishing theconnection with the AP 300. Further, the UE 100 determines whether theoffload is continued or canceled after the offload is started. Thus, theabove ping-pong phenomenon can be avoided by maintaining withoutreleasing the RRC connection even when the offload is started.

In the first embodiment, the UE 100 carries out the determination on thebasis of the communication status with the AP 300. Thus, the UE 100 canrespond to change in the communication status with the AP 300 after theoffload.

In the operation pattern 1, the UE 100 receives from the eNB 200, beforethe RRC connection is released, the idle time configuration informationfor configuration of the operation of the UE 100 after the RRCconnection is released. Thereby, the UE 100 can performs the properoperation after the RRC connection is released (that is, in the idlestate).

In the operation pattern 1, the UE 100 transmits the notificationindicating that the offload is continued, to the eNB 200, when it isdetermined that the offload is continued. Then, the UE 100 releases theRRC connection after the notification is transmitted. Thereby, the UE100 can voluntarily release the RRC connection in a case where there isno problem releasing the RRC connection. In addition, cellular resourceis saved by releasing the RRC connection.

In the operation pattern 1, the UE 100 cancels the offload and discardsthe idle time configuration information when it is determined that theoffload is canceled. Thereby, memory can be saved by discardingunnecessary idle time configuration information.

In the operation pattern 2, the UE 100 transmits, to the eNB 200, thetransmission stop request for requesting to stop transmitting the RRCrelease message before the offload is started. Thereby, the UE 100 canprevent the eNB 200 from releasing the RRC connection.

In the operation pattern 2, the UE 100 transmits to the eNB 200 thetransmission request to request to transmit the RRC release message whenit is determined that the offload is continued, and the UE 100 receivesthe RRC release message from the eNB 200. Thereby, the UE 100 canvoluntarily release the RRC connection in a case where there is noproblem releasing the RRC connection. Also, the RRC release messageincludes the idle time configuration information. Thus, the UE 100 canperforms the proper operation after the RRC connection is released (thatis, in the idle state).

[Second Embodiment]

The second embodiment will be described while focusing on the differencefrom the first embodiment. Operation environment according to the secondembodiment is similar to that of the first embodiment.

(Operation According to Second Embodiment)

In the above first embodiment, the timer comprised by each of the UE 100and the eNB 200 is not described in detail. The second embodiment is anembodiment in which these timers are focused. As described above, the UE100 comprises a terminal-side timer (hereinafter called an “UE timer”)that regulates a connection maintaining period during which the RRCconnection should be maintained after the offload is started. The UE 100activates the terminal-side timer when the offload is started (refer tostep S104 in FIG. 8 and step S204 in FIG. 9). Then, the UE 100 maintainsthe RRC connection until the UE timer expires.

On the other hand, the eNB 200 comprises a base station-side timer(hereinafter called an “eNB timer”) that regulates a connectionmaintaining period during which the RRC connection should be maintainedafter transmission and reception of traffic with the UE 100 is stopped.This eNB timer may be called an Inactivity timer. The eNB 200 activatesthe eNB timer when transmission and reception of traffic with the UE 100is stopped. Further, the eNB 200 maintains the RRC connection until theeNB timer expires, transmits the RRC release message to the UE 100 whenthe eNB timer expires, and then releases the RRC connection.

Here, there is a possibility that competition occurs between the UEtimer and the eNB timer. Specifically, in a case where the connectionmaintaining period set to the eNB timer is shorter than the connectionmaintaining period set to the UE timer, the eNB timer expires before theUE timer expires, and then the eNB 200 releases the RRC connection.Hereinafter, operation according to the second embodiment for resolvingthis defect will be described.

(1) Operation Pattern 1 According to the Second Embodiment

The operation pattern 1 according to the second embodiment is a patternin which a suitable connection maintaining period is preliminarily setto the UE timer. Specifically, the connection maintaining period set tothe UE timer is equal to or shorter than the connection maintainingperiod set to the eNB timer. In other words, the connection maintainingperiod set to the eNB timer is equal to or longer than the connectionmaintaining period set to the UE timer. Thus, the eNB timer can beprevented from expiring before the UE timer expires.

(2) Operation Pattern 2 According to the Second Embodiment

The operation pattern 2 according to the second embodiment is a patternin which the UE transmits and receives the traffic with the AP 300 andtransmits and receives the traffic with the eNB 200 to prevent the eNBtimer from expiring (or to stop the eNB timer) after the offload isstarted.

For example, “the UE transmits and receives the traffic with the eNB 200to prevent the eNB timer from expiring” means an operation in which apart of traffic (bearers) is left for the eNB 200. This operation canbasically apply in a case where the UE 100 uses a plurality of servicesvia the eNB 200. However, the connection state may be maintained bygenerating dummy traffic (keep arrive message) and periodicallytransmitting the dummy traffic to the eNB 200 even when the UE 100 usesonly one service. The keep arrive message may be a message of upperlayer (for example, a message transmitted to a server owned by anoperator) or a message of lower layer (for example, a message exchangedamong the MAC layer).

FIG. 10 is a sequence diagram of the operation pattern 2 according tothe second embodiment. In the present sequence, an operation in which apart of traffic is left for the eNB 200 will be described as an example.In an initial state of the present sequence, the UE 100 is in a state inwhich the UE 100 has established the RRC connection (the firstconnection) with the eNB 200 (in step S301).

As shown FIG. 10, in step S302, when the UE 100 decides that the offloadis started, the UE 100 selects traffic which is left for the eNB 200. Aselection criterion is QoS type or service type and the like. Forexample, the UE 100 may determine that operator-unique service (serviceunique to an operator line that cannot be provided via the WLAN) ispreferentially left for the eNB 200.

In step S303, the UE 100 establishes a connection (a second connection)with the AP 300 and then the offload is started. Specifically, the UE100 switches traffic other than traffic which is left for the eNB 200from traffics transmitted and received with the eNB 200 so as to betransmitted and received with the AP 300.

The UE 100 and the eNB 200 maintain without releasing the RRC connectioneven when the offload is started. Thus, the UE 100 maintains theconnection state of the cellular communication without transition to theidle state of the cellular communication even when the offload isstarted.

In step S304, the UE 100 activates the UE timer in response to the startof the offload.

In step S305, the UE 100 determines whether the offload is continued ornot. A method of determination is the same as that of the firstembodiment.

When it is determined that the offload is canceled (in step S305: No),the UE 100 cancels the offload in step S306. In other words, the UE 100switches the traffic transmitted and received with the AP 300 so as tobe transmitted and received with the eNB 200. Also, the UE 100 mayrelease the connection of the AP 300.

On the other hand, in a case where it is determined that the offload iscontinued (in step S305: Yes) and when the UE timer expires (in stepS307), the UE 100 switches the traffic which is left for the eNB 200 soas to be transmitted and received with the AP 300 in step S308.

The eNB 200 activates the eNB timer in response to the traffic of the UE100 having been lost, and then the eNB timer expires.

In step S309, the eNB 200 transmits the RRC release message to the UE100. The RRC release message includes the idle time configurationinformation for configuration of an operation of the UE 100 after theRRC connection is released. As a result, the UE 100 and the eNB 200release the RRC connection. Further, the UE 100 transits from theconnection state of the cellular communication to the idle state (instep S310). Then, the UE 100 performs an operation in the idle state onthe basis of the idle time configuration information.

(3) Operation Pattern 3 According to the Second Embodiment

The operation pattern 3 according to the second embodiment is a patternin which the eNB 200 inquires the UE 100 of whether it is possible torelease the RRC connection in a case where the release request for theRRC connection is not received from the UE 100 when the eNB timerexpires in the eNB 200. In other words, the eNB 200 cannot release theRRC connection until an approval is gained from the UE 100.

FIG. 11 is a sequence diagram of the operation pattern 3 according tothe second embodiment. In an initial state of the present sequence, theUE100 is in a state in which the UE100 has established the RRCconnection (the first connection) with the eNB 200.

As shown FIG. 11, in step S401, when the UE 100 decides on starting ofthe offload, the UE 100 transmits an offload notification to that effectto the eNB 200.

In step S402, the eNB 200 transmits an acknowledgment (an Ack) to the UE100 in response to a receipt of the offload notification from the UE100.

In step S403, the UE 100 establishes a connection (a second connection)with the AP 300 in response to a receipt of the Ack from the eNB 200,and then the UE 100 starts the offload. Specifically, the UE 100switches the traffic transmitted and received with the eNB 200 so as tobe transmitted and received with the AP 300. In addition, the UE 100activates the UE timer in a response to the start of the offload.

The UE 100 and the eNB 200 maintain without releasing the RRC connectioneven when the offload is started. Thus, the UE 100 maintains theconnection state of the cellular communication without transition to theidle state of the cellular communication even when the offload isstarted.

In step S404, the eNB 200 activates the eNB timer in response to thetraffic of the UE 100 having been lost.

In step S405, the eNB timer expires. In step S406, the eNB 200 transmitsrelease request for the RRC connection to the UE 100 when the eNB timerexpires. The release request corresponds to an inquiring of whether itis possible to release the RRC connection. Also, the release request canbe regarded as a notification indicating that the eNB timer expires.

In step S407, the UE 100 determines whether the release request for theRRC connection received from the eNB 200. Since, during the UE timerrunning, the UE 100 carries out the determination whether the offload iscontinued or not, the UE 100 determines that the RRC release request isrejected when the UE 100 receives the release request for the RRCconnection from the eNB 200 during the UE timer running. On the otherhand, UE 100 determines that the RRC release request is accepted whenthe UE 100 receives the release request for the RRC connection from theeNB 200 after the UE timer expires.

In step S408, the UE 100 transmits, to the eNB 200, a determinationresult of whether the release request for the RRC connection is acceptedor rejected. The UE 100 transmits an Ack to the eNB 200 in a case wherethe release request for the RRC connection is accepted, and transmits aNack to the eNB 200 in a case where the release request for the RRCconnection is rejected.

In step S409, the eNB 200 verifies whether the Ack has been received orthe Nack has been received from the UE 100.

When the Ack has been received from the UE 100 (in step S409: Yes), theeNB 200 transmits the RRC release message to the UE 100 in step S410.

On the other hand, when the Nack has been received from the UE 100 (instep S409: No), the eNB 200 restarts the eNB timer in step S411. Theconnection maintaining period set to the eNB timer in the restart may bethe same as the initial connection maintaining period, or may bedifferent from the initial connection maintaining period (for instance,a connection maintaining period shorter than the initial connectionmaintaining period).

(4) Operation Pattern 4 According to the Second Embodiment

The operation pattern 4 according to the second embodiment is a patternin which the eNB 200 controls the eNB timer in order to prevent the eNBtimer from expiring before the UE timer expires. There are the followingthree methods (operation patterns 4-1 to 4-3) as a method of controllingthe eNB timer.

In the operation pattern 4-1 according to the second embodiment, the eNBtimer includes a general eNB timer (a first eNB timer) used for apurpose of other than the offload and an offload eNB timer (a second eNBtimer) used for a purpose of the offload. A connection maintainingperiod set to the offload eNB timer is equal to or longer than theconnection maintaining period notified to the UE 100. The eNB 200selects the offload eNB timer and then activates the offload eNB timerin response to the start of the offload.

In the operation pattern 4-2 according to the second embodiment, the eNB200 notifies the UE 100 of the connection maintaining period that shouldbe set to the UE timer. It is preferable that this notification is anotification by broadcasting (for example, a notification by the SIB).However, this notification may be a notification by unicasting. The eNB200 sets a connection maintaining period equal to or longer than theconnection maintaining period notified to the UE 100, to the eNB timer.

In the operation pattern 4-3 according to the second embodiment, the eNB200 cancels the activation of the eNB 200 timer in response to the startof the offload. In this case, the eNB 200 may set the connectionmaintaining period equal to or longer than the connection maintainingperiod set to the UE timer, to the eNB timer in a case where the eNB 200knows the connection maintaining period set to the UE timer.Alternatively, as described in the first embodiment, the releaseprocessing of the RRC connection may be performed at the initiative ofthe UE.

Also, in the operation patterns 4-2 and 4-3 according to the secondembodiment, the eNB 200 may acquire information indicating theconnection maintaining period set to the UE timer from the UE 100. Inthis case, for example, the UE 100 may include information indicatingthe connection maintaining period set to the UE timer in the UECapability message, for instance, and transmit the information to theeNB 200.

FIG. 12 is a sequence diagram of the operation pattern 4 according tothe second embodiment. The operation pattern 4-2 is mainly assumed here.In an initial state of the present sequence, the UE100 is in a state inwhich the UE100 has established the RRC connection (the firstconnection) with the eNB 200.

As shown in FIG. 12, in step S501, the eNB 200 transmits the informationindicating the connection maintaining period that should be set to theUE timer to the UE 100 by broadcasting. The UE 100 sets the connectionmaintaining period indicated by the information received from the eNB200 to the UE timer.

In step S502, when the UE 100 decides on starting of the offload, the UE100 transmits an offload notification to that effect to the eNB 200.

In step S503, the eNB 200 transmits an acknowledgment (an Ack) to the UE100 in response to a receipt of the offload notification from the UE100.

In step S504, the eNB 200 sets the connection maintaining period equalto or longer than the connection maintaining period set to the UE timerto the eNB timer. Also, step S504 may be between step S501 and step S502or between step S502 and step S503.

In step S505, the UE 100 establishes the connection (the secondconnection) with the AP 300 in response to a receipt of the Ack from theeNB 200, and then the offload is started. Specifically, the UE 100switches the traffic transmitted and received with the eNB 200 so as tobe transmitted and received with the AP 300.

The UE 100 and the eNB 200 maintain without releasing the RRC connectioneven when the offload is started. Thus, the UE 100 maintains theconnection state of the cellular communication without transition to theidle state of the cellular communication even when the offload isstarted.

In step S506, the UE 100 activates the UE timer in response to the startof the offload.

In step S507, the eNB 200 activates the eNB timer in response to thetraffic of the UE 100 having been lost.

In step S508, during the UE timer running, the UE 100 carries out thedetermination whether the offload is continued or not. A method ofdetermination is the same as that of the first embodiment.

When it is determined that the offload is canceled (in step S508: No),the UE 100 cancels the offload in step S509. In other words, the UE 100switches the traffic transmitted and received with the AP 300 so as tobe transmitted and received with the eNB 200. Also, the UE 100 mayrelease the connection of the AP 300.

In step S510, the UE timer expires.

In step S511, the eNB timer expires. Timing of the eNB timer expiring islater than timing of the UE timer expiring.

In step S512, the eNB 200 transmits the RRC release message to the UE100 in a response to the expiration of the eNB timer. The RRC releasemessage includes the idle time configuration information forconfiguration of an operation of the UE 100 after the RRC connection isreleased. As a result, the UE 100 and the eNB 200 release the RRCconnection. Further, the UE 100 transits from the connection state ofthe cellular communication to the idle state (in step S513). Then, theUE 100 performs an operation in the idle state on the basis of the idletime configuration information.

(Conclusion of the Second Embodiment)

In the operation pattern 1 according to the second embodiment, theconnection maintaining period set to the UE timer is equal to or shorterthan the connection maintaining period set to the eNB timer. Thus, theeNB timer is prevented from expiring before the UE timer expires withoutmodifying the existing eNB timer.

In the operation pattern 2 according to the second embodiment, the UE100 transmits and receives the traffic with the AP 300 and transmits andreceives the traffic with the eNB 200 to prevent the eNB timer fromexpiring (or to stop the eNB timer) after the offload is started. Thus,the eNB timer is prevented from expiring before the UE timer expireswithout modifying the existing eNB timer.

In the operation pattern 3 according to the second embodiment, the eNB200 inquires the UE 100 of whether it is possible to release the RRCconnection in a case where the release request for the RRC connection isnot received from the UE 100 when the eNB timer expires in the eNB 200.Thus, the RRC connection is prevented from being unexpectedly releasedbecause even though the eNB timer expires before the UE timer expires,the RRC connection is not released until the approval is gained from theUE 100.

In the operation pattern 4 according to the second embodiment, the eNB200 controls the eNB timer in order to prevent the eNB timer fromexpiring before the UE timer expires. Thus, the eNB timer is preventedfrom expiring before the UE timer expires.

[Third Embodiment]

Next, a third embodiment will be described.

A case is assumed where the communication state of each of the eNB 200and the AP 300 is compared by the UE 100 so that the UE 100 itself iscapable of selecting the connection target from the eNB 200 and the AP300.

In this case, the plurality of UEs 100 may select the same AP 300 as aconnection target, and may simultaneously start a connection process onthe AP 300. Therefore, due to the conflict from the connection process,some UEs 100 may not establish a connection with the AP 300.

Further, even when all of these UEs 100 are capable of establishing aconnection with the AP 300, there are problems that as a result of anincrease in load level of the AP 300, it is not possible to ensure asufficient throughput and too many unused resources of the eNB 200occur.

Thus, an object of the third embodiment is to resolve a problem causeddue to simultaneous connection by the plurality of UEs 100 to the AP300.

(Operation according to third embodiment)

An operation according to the third embodiment will be described.

(1) Operation Environment

FIG. 13 is a diagram for describing an operation environment accordingto the third embodiment.

As shown in FIG. 13, there are a plurality of UEs 100 in a coverage ofthe eNB 200 and in a transport T such as a train or a bus. The transportT moves along a predetermined route (a railway or a road).

The UE 100 has established a connection with the eNB 200, and performscellular communication with the eNB 200. Specifically, the UE 100transmits and receives a cellular radio signal including a traffic (userdata) with the eNB 200. Alternatively, some UEs 100 may not establish aconnection with the eNB 200.

Further, the AP 300 is provided in a coverage of the eNB 200. The AP 300is an AP (Operator controlled AP) managed by an operator. Specifically,the AP 300 is provided at a stop point (a station or a stop, etc.) atwhich the transport T stops.

It is noted that in the third embodiment, a case is assumed where thecommunication state of each of the eNB 200 and the AP 300 is compared bythe UE 100 so that the UE 100 itself is capable of selecting theconnection target from the eNB 200 and the AP 300.

In such an operation environment, when the transport T moves into thecoverage of the AP 300 (movement 1), the plurality of UEs 100 in thetransport T start a connection process to the AP 300. The UE 100 thathas established the connection with the AP 300 releases the connectionwith the eNB 200.

Further, the transport T moves out of the coverage of the AP 300(movement 2) after stopping at the stop point. At that time, theplurality of UEs 100 in the transport T release the connection with theAP 300 and establish the connection with the eNB 200.

Thus, in an operation environment where the AP 300 is provided at thestop point (a station or a stop, etc.) at which the transport T stops,when the UE 100 itself is capable of selecting the connection targetfrom the eNB 200 and the AP 300, there may occur an ineffectiveoperation in which the

UE 100 switches the connection from the eNB 200 to the AP 300, andthereafter, the UE 100 switches the connection from the AP 300 to theeNB 200. Further, when the plurality of UEs 100 simultaneously performthe connection process, there may be a conflict from the connectionprocess.

An operation for resolving such a problem will be described, below.

(2) UE Operation Flow

FIG. 14 is an operation flow diagram of the UE 100 according to thethird embodiment. Here, a case is assumed where the WLAN communicationunit 112 of the UE 100 is in an on state. In the third embodiment, whenthe WLAN communication unit 112 is in an on state, the processor 160 ofthe UE 100 measures a movement speed (hereinafter, “UE movement speed”)of the UE 100, on the basis of the location information evaluated fromthe GNSS receiver 130, for example. It is noted that when anacceleration sensor is provided in the UE 100, the UE movement speed(acceleration) may be measured by the acceleration sensor.

As shown in FIG. 14, in step S601, the processor 160 determines whetheror not the UE movement speed rapidly decreases. The “UE movement speedrapidly decreasing” means that an amount of decrease in UE movementspeed per unit time exceeds a constant amount.

It is noted that the processor 160 executes a process in step S601 whenit is detected that the UE movement speed is high speed, and otherwise,may not execute the process in step S601. This is because the UE 100being located in the transport T is a prerequisite of step S601.

When the UE movement speed rapidly decreases (step S601: Yes), in stepS602, the processor 160 activates a timer that regulates a period of anAP connection restriction in which the connection by the WLANcommunication unit 112 with the AP 300 is restricted (hereinafter, “APconnection restriction timer”). It is noted that the period of an APconnection restriction (that is, a timer value of the AP connectionrestriction timer) may be previously stored in the memory 150, and maybe designated by the eNB 200 to the UE 100.

In the period of an AP connection restriction, the processor 160switches the WLAN communication unit 112 to an off state. Alternatively,the processor 160 may cancel decoding the beacon signal of the AP 300 ortransmitting to the AP 300 while maintaining the WLAN communication unit112 in an on state.

In step S603, the processor 160 determines whether or not the UEmovement speed rapidly increases. The “UE movement speed rapidlyincreasing” means that an amount of increase in UE movement speed perunit time exceeds a constant amount.

When the UE movement speed rapidly increases (step S603: Yes), in stepS605, the processor 160 cancels the AP connection restriction. That is,it is made possible to connect with the AP 300.

On the other hand, when the UE movement speed does not rapidly increase(step S603: No), in step S604, the processor 160 confirms whether or notthe AP connection restriction timer expires. When the AP connectionrestriction timer expires (step S604: Yes), in step S605, the processor160 cancels the AP connection restriction. On the other hand, when theAP connection restriction timer does not expire (step S604: No), theprocessor 160 returns the process to step S603.

(Summary of Third Embodiment)

The UE 100 according to the third embodiment measures the UE movementspeed when the WLAN communication unit 112 is in an on state. Upondetection of a rapid decrease in UE movement speed, the UE 100 restrictsthe start of connection by the WLAN communication unit 112 with the AP300. As a result, in an operation environment as shown in FIG. 13, it ispossible to avoid an ineffective operation in which the UE 100 switchesthe communication from the eNB 200 to the AP 300, thereafter, the UE 100switches the connection from the AP 300 to the eNB 200. Further, it ispossible to avoid the conflict from the connection process caused whenthe plurality of UEs 100 simultaneously perform the connection process.

In the third embodiment, when detecting a rapid increase in UE movementspeed after detecting a rapid decrease in UE movement speed, the UE 100cancels the restriction of a start of connection by the WLANcommunication unit 112 with the AP 300. As a result, it is possible toreturn to a normal operation from a state of the AP connectionrestriction.

[Modification of Third Embodiment]

FIG. 15 is a sequence diagram according to a modification of the thirdembodiment.

As shown in FIG. 15, the processor 240 of the eNB 200 transmits, to theUE 100, a list of APs 300 that should be subject to a connectionrestriction (hereinafter, “AP blacklist”). The AP blacklist includes anidentifier of the AP 300 provided at a stop point (a station or a stop,etc.) at which the transport T stops, for example. The identifier of theAP 300 (AP identifier) is an SSID (Service Set Identifier) or a BSSID(Basic Service Set Identifier).

From a viewpoint of a usage efficiency of a radio resource, theprocessor 240 may transmit the AP blacklist to the UE 100 by broadcast.Further, the processor 240 may periodically transmit the AP blacklist.Alternatively, the eNB 200 may receive, from the UE 100, informationindicating whether the WLAN communication unit 112 is in an on state,and may transmit the AP blacklist by unicast to the UE 100 in which theWLAN communication unit 112 is in an on state.

The cellular communication unit 111 of the UE 100 receives the APblacklist from the eNB 200. The memory 150 stores the AP blacklist. Whenan AP identifier included in the beacon signal received by the WLANcommunication unit 112 from the AP 300 matches an AP identifier in theAP blacklist, the processor 160 restricts the start of connection withthe AP 300.

However, it is necessary that such a method is not applied to the UE 100other than the UE 100 located in the transport T. Therefore, theprocessor 160 may enable the AP blacklist in the memory 150 whendetecting that the UE movement speed rapidly decreases, and otherwise,disable the AP blacklist.

Alternatively, when an AP identifier included in the beacon signalreceived by the WLAN communication unit 112 from the AP 300 matches anAP identifier in the AP blacklist, the processor 160 restricts a startof connection with the AP 300 during a constant period, and after theconstant period passes, may cancel the connection restriction. Such aconstant period may be regulated on the basis of an average time periodduring which the transport T stops at the stop point (a station or astop, etc.).

[Fourth Embodiment]

Description about a fourth embodiment proceeds with a focus on adifference from the above-described third embodiment.

In the fourth embodiment, an operation flow of the UE 100 is differentfrom that in the third embodiment. It is noted that a systemconfiguration and an operation environment in the fourth embodiment arein much the same way as in the third embodiment.

FIG. 16 is an operation flow diagram of the UE 100 according to thefourth embodiment. Here, a case is assumed where the WLAN communicationunit 112 of the UE 100 is in an on state. In the fourth embodiment, whenthe WLAN communication unit 112 is in an on state, the processor 160 ofthe UE 100 measures the reception level of the beacon signal received bythe WLAN communication unit 112 from the AP 300 (hereinafter, “APreception level”).

As shown in FIG. 16, in step S701, the processor 160 determines whetheror not the AP reception level rapidly increases. The “AP reception levelrapidly increasing” means that an amount of increase in AP receptionlevel per unit time exceeds a constant amount.

When the AP reception level rapidly increases (step S701: Yes), in stepS702, the processor 160 activates the AP connection restriction timer.As described above, the period of an AP connection restriction (that is,a timer value of the AP connection restriction timer) may be previouslystored in the memory 150, and may be designated by the eNB 200 to the UE100.

In the fourth embodiment, in the period of an AP connection restriction,the processor 160 may cancel decoding the beacon signal of the AP 300 ortransmitting the beacon signal to the AP 300 while maintaining the WLANcommunication unit 112 in an on state. That is, although it is notpossible to connect with the AP 300, it is made possible to measure theAP reception level.

In step S703, the processor 160 determines whether or not the APreception level rapidly decreases. The “AP reception level rapidlydecreasing” means that an amount of decrease in AP reception level perunit time exceeds a constant amount.

When the AP reception level rapidly decreases (step S703: Yes), in stepS705, the processor 160 cancels the AP connection restriction. That is,it is made possible to connect with the AP 300.

On the other hand, when the AP reception level does not rapidly decrease(step S703: No), in step S704, the processor 160 confirms whether or notthe AP connection restriction timer expires. When the AP connectionrestriction timer expires (step S704: Yes), in step S705, the processor160 cancels the AP connection restriction. On the other hand, when theAP connection restriction timer does not expire (step S704: No), theprocessor 160 returns the process to step S703.

(Summary of fourth embodiment) The UE 100 according to the fourthembodiment measures the AP reception level when the WLAN communicationunit 112 is in an on state. When detecting a rapid increase in APreception level, the UE 100 restricts the start of connection by theWLAN communication unit 112 with the AP 300. As a result, in anoperation environment as shown in FIG. 13, it is possible to avoid anineffective operation in which the UE 100 switches the communicationfrom the eNB 200 to the AP 300, thereafter, the UE 100 switches theconnection from the AP 300 to the eNB 200. Further, it is possible toavoid the conflict from the connection process caused when the pluralityof UEs 100 simultaneously perform the connection process.

In the fourth embodiment, when detecting a rapid decrease in APreception level after detecting a rapid increase in AP reception level,the UE 100 cancels the restriction of a start of connection by the WLANcommunication unit 112 with the AP 300. As a result, it is possible toreturn to a normal operation from a state of the AP connectionrestriction.

[Modification of Fourth Embodiment]

In the fourth embodiment also, the AP blacklist may be applied in muchthe same way as in the above-described third embodiment. However, it isnecessary that the AP blacklist is not applied to the UE 100 other thanthe UE 100 located in the transport T. Therefore, when detecting a rapidincrease in AP reception level, the processor 160 may enable the APblacklist in the memory 150, and otherwise, disable the AP blacklist.

Alternatively, as described above, when an AP identifier included in thebeacon signal received by the WLAN communication unit 112 from the AP300 matches an AP identifier in the AP blacklist, the processor 160restricts the start of connection with the AP 300 during a constantperiod, and after the constant period passes, may cancel the connectionrestriction.

[Fifth Embodiment]

Next, a fifth embodiment will be described.

Generally, the UE 100 performs a WLAN scan in order to discover aconnectable AP 300. The WLAN scan is an operation in which reception ofa WLAN radio signal (for example, a beacon signal) is attempted by theWLAN communication unit 112 for each WLAN channel.

The UE 100 continues the WLAN scan while switching the WLAN channelsuntil it is completed to attempt all the WLAN channels or until it issuccessful to receive the WLAN radio signal. Thus, the power consumptionof the UE 100 (in particular, the power consumption of the WLANcommunication unit 112) increases.

Therefore, there is a problem that in an offload, the power consumptionof the UE 100 increases resulting from the WLAN scan.

Therefore, an object of the fifth embodiment is to enable realization ofan offload of the eNB 200 while restraining an increase in powerconsumption resulting from the WLAN scan.

(System Configuration)

FIG. 17 is a system configuration diagram according to the fifthembodiment.

As shown in FIG. 17, the EPC 20 includes an E-SMLC (Evolved ServingMobile Location Centre) 600 that is a serve device that provideslocation information indicating a geographical location of the UE 100.The E-SMLC 600 collects a result of a radio measurement in the UE 100and/or the eNB 200 to calculate location information indicating ageographical location of the UE 100. For details of a mechanism forcalculating the location information, refer to 3GPP technicalspecification “TS 36.305”.

(Operation According to Fifth Embodiment)

Next, an operation according to the fifth embodiment will be described.

(1) Operation Environment

FIG. 18 is a diagram for describing an operation environment accordingto the fifth embodiment. As shown in FIG. 18, the AP 300 is provided ina coverage of the eNB 200. The AP 300 is an AP (Operator controlled AP)managed by an operator.

Further, the UE 100 is located in the coverage of the eNB 200 and in thecoverage of the AP 300. The UE 100 has established a connection with theeNB 200, and performs cellular communication with the eNB 200.Specifically, the UE 100 transmits and receives a cellular radio signalincluding a traffic (user data) with the eNB 200. It is noted that inFIG. 18, there shows only one UE 100 that have established theconnection with the eNB 200; in a real environment, a large number ofUEs 100 may have established the connection with the eNB 200.

When the eNB 200 establishes a connection with a large number of UEs100, a load level of the eNB 200 increases. The “load level” means thedegree of congestion in the eNB 200 such as a traffic load of the eNB200 or usage of radio resources of the eNB 200. Here, at least a part oftraffic transmitted and received between the UE 100 and the eNB 200 isallowed to transfer to the WLAN system, so that it is possible todisperse a traffic load of the eNB 200, in the WLAN system.

Description will be provided for an operation for transferring(offloading) the traffic transmitted and received between the UE 100 andthe eNB 200, to the WLAN system below. It is noted that the offloadincludes not only a case where all the traffics transmitted and receivedbetween the UE 100 and the eNB 200 are transferred to the WLAN systembut also a case where at least a part of the traffic is transferred tothe WLAN system while maintaining a connection between the UE 100 andthe eNB 200.

(2) WLAN Scan

Prior to description of the offload operation, a general WLAN scan willbe described.

The UE 100 performs a WLAN scan in order to discover a connectable AP300. The WLAN scan is an operation in which reception of a WLAN radiosignal from the AP 300 is attempted by the WLAN communication unit 112for each WLAN channel. The WLAN scan includes a passive scan scheme andan active scan scheme; in the fifth embodiment, either scheme may beselected.

The passive scan scheme is a scheme in which the UE 100 attempts toreceive the beacon signal periodically transmitted in the WLAN channelemployed by the AP 300. The beacon signal includes information on the AP300, such as an identifier of the AP 300. The identifier of the AP 300is an SSID (Service Set Identifier) or a BSSID (Basic Service SetIdentifier). The UE 100 attempts to receive the beacon signal over apredetermined time equal to or longer than a transmission period of thebeacon signal, for each WLAN channel. When a predetermined time passesor when it is not successful to receive the beacon signal within apredetermined time, the UE 100 switches to a next WLAN channel, andthen, attempts to receive the beacon signal again.

The active scan scheme is a scheme in which the UE 100 transmits a proberequest in the WLAN channel, the AP 300 that is employing the WLANchannel transmits a probe response in response to the probe request, andthe UE 100 attempts to receive the probe response. Information includedin the probe response is similar to the information included in thebeacon signal. Therefore, it is possible to regard the probe response asone type of the beacon signal. The UE 100 attempts to receive the proberesponse over a predetermined time since transmitting the probe request,for each WLAN channel. When a predetermined time passes or when it isnot successful to receive the probe response within a predeterminedtime, the UE 100 switches to a next WLAN channel, and transmits theprobe request again, and then, attempts to receive the probe response.

Thus, the UE 100 continues the WLAN scan while switching the WLANchannels until it is successful to receive at least the beacon signal(or the probe response), and thus, the power consumption of the UE 100(in particular, the power consumption of the WLAN communication unit112) increases. Therefore, in the offload operation according to thefifth embodiment, when the WLAN scan is made efficient, the powerconsumption in the WLAN scan is reduced.

(3) Offload Operation

FIG. 19 is a sequence diagram of the offload operation according to thefifth embodiment. In an initial state of the present sequence, the UE100 has established the connection with the eNB 200, and brings the WLANcommunication unit 112 into an off state (a state where it is notpossible to transmit and receive the WLAN radio signal). Further, it isassumed that the load level of the eNB 200 is high and a preferablesituation is realized to perform the offload, for example.

As shown in FIG. 19, in step S801, the processor 160 of the UE 100notifies the eNB 200 by the cellular communication unit 111 ofinformation indicating a WLAN communication capability (hereinafter,“WLAN capability information”) of the UE 100. The WLAN capabilityinformation is information indicating whether or not the UE 100 supportsthe WLAN communication. When the UE 100 supports the WLAN communication,the WLAN capability information may include information indicating afunction of the supported WLAN communication (hereinafter, “WLANfunction information”). Examples of the function of the supported WLANcommunication include a standard of the supported WLAN communication(IEEE 802.11a/b/g/n), a supported QoS function (WMM: Wi-Fi MultiMedia,etc.), and a support WLAN frequency band (2.4 GHz band, 5 GHz band,etc.).

It is noted that the UE 100 may autonomously notify the eNB 200 of theWLAN capability information during connection with the eNB 200, and maynotify the eNB 200 of the WLAN capability information in response to arequest from the eNB 200 after connection with the eNB 200.

When the cellular communication unit 210 receives the WLAN capabilityinformation, the processor 240 of the eNB 200 determines, on the basisof the received WLAN capability information, whether or not the UE 100is an offloadable UE 100 (that is, the UE 100 that supports the WLANcommunication). Further, the processor 240 may determine that the UE 100is not possible to offload when there is no AP 300 that matches the WLANfunction information, out of the APs 300 in the coverage of the eNB 200.In this case, description is provided on the assumption that it isdetermined that the UE 100 is possible to offload.

In step S802, the processor 160 of the UE 100 notifies the eNB 200, bythe cellular communication unit 111, of information indicating that theWLAN communication unit 112 is in an off state (hereinafter, “WLAN offinformation”). The processor 160 may notify the eNB 200 of the WLAN offinformation when bringing the WLAN communication unit 112 into an offstate, and may notify the eNB 200 of the WLAN off information inresponse to an inquiry from the eNB 200. Alternatively, the processor160 may periodically notify the eNB 200 whether the WLAN communicationunit 112 is in an off state or an on state.

In step S803, the processor 240 of the eNB 200 acquires informationindicating an operation status of the AP 300 (hereinafter, “AP operationinformation”), by the network interface 220, from the AP 300. The APoperation information includes information indicating a WLAN channeloperating in the AP 300 and information indicating a WLAN frequency bandincluding the WLAN channel. Further, the AP operation information mayinclude information indicating a timing (period) at which the AP 300transmits the beacon signal. The AP 300 may periodically notify the eNB200 of the AP operation information, and may notify the eNB 200 of theAP operation information in response to a request from the eNB 200. Thenotification may be performed by way of a core network.

In step S804, the processor 240 of the eNB 200 acquires informationindicating a geographical location of the UE 100 (hereinafter, “UElocation information”), by the network interface 220, from the E-SMLC600. Alternatively, when the UE 100 has the GNSS receiver 130 and theGNSS receiver 130 is in an on state, the processor 240 may acquire, bythe cellular communication unit 111, the UE location informationgenerated by using the GNSS receiver 130, from the UE 100.

It is noted that step S801 to step S804 may be performed in any order aswell as in this order.

In step S805, the processor 240 of the eNB 200 compares the UE locationinformation and information indicating a geographical location of the AP300 (hereinafter, “AP location information”) to determine whether or notthe UE 100 comes close to the AP 300. Specifically, the processor 240determines whether or not the UE 100 is located in the coverage of theAP 300. It is noted that the AP location information may be previouslystored in the memory 230 of the eNB 200 and may be notified to the eNB200 from the AP 300. In this case, description is provided on theassumption that it is determined that the UE 100 comes close to the AP300.

The processor 240 of the eNB 200 determines the UE 100 as the UE 100subject to offload because the UE 100 that supports the WLANcommunication brings the WLAN communication unit 112 in an off state andcomes close to the AP 300. Then, the processor 240 generates scancontrol information for controlling the WLAN scan by the UE 100, on thebasis of the AP operation information. It is noted that when the scancontrol information is generated, the WLAN capability information, inaddition to the AP operation information, may be taken intoconsideration.

The scan control information includes at least one of information on ascan frequency and information on a scan time. Further, the scan controlinformation may include information on a priority (priorityinformation).

The information on the scan frequency includes channel information fordesignating a WLAN channel subject to the WLAN scan or a WLAN channelnot subject to the WLAN scan. The WLAN channel subject to the WLAN scanis a WLAN channel operating in the AP 300 near the UE 100. The WLANchannel not subject to the WLAN scan is a WLAN channel not operating inthe AP 300 near the UE 100.

Further, the information on the scan frequency includes frequency bandinformation for designating a WLAN frequency band subject to the WLANscan or a WLAN frequency band not subject to the WLAN scan.

The WLAN frequency band subject to the WLAN scan is a WLAN frequencyband operating in the AP 300 near the UE 100. The WLAN frequency bandnot subject to the WLAN scan is a WLAN frequency band not operating inthe AP 300 near the UE 100.

The priority information is information for designating a WLAN channeland/or a WLAN frequency band where reception of the WLAN radio signal(beacon signal, etc.) should be preferentially attempted in the WLANscan. It is preferable to set the priority information so that the WLANchannel operating in the AP 300 near the UE 100 and/or the operatingWLAN frequency band is preferentially scanned.

The information on the scan time includes period information fordesignating a period during which the WLAN scan should be continued(that is, a period during which the WLAN should be maintained in an onstate).

Further, the information on the scan time includes timing informationfor designating a timing at which the WLAN scan should be performed. Thetiming information preferably is information indicating a timing(period) at which the AP 300 near the UE 100 transmits the beaconsignal.

In step S806, the processor 240 of the eNB 200 transmits, by thecellular communication unit 210, a WLAN on request for switching theWLAN communication unit 112 to an on state, to the UE 100. The processor240 transmits the scan control information to be included in the WLAN onrequest. The cellular communication unit 111 of the UE 100 receives theWLAN on request.

In step S807, the processor 160 of the UE 100 switches the WLANcommunication unit 112 to an on state, in response to reception of theWLAN on request. Then, after switching the WLAN communication unit 112to an on state, the processor 160 controls the WLAN scan in accordancewith the scan control information included in the WLAN on request.

Specifically, the processor 160 performs the WLAN scan only on the WLANchannel subject to the WLAN scan, on the basis of the channelinformation, and performs the WLAN scan only on the WLAN frequency bandsubject to the WLAN scan, on the basis of the frequency bandinformation. Further, on the basis of the priority information, theprocessor 160 preferentially attempts to receive the WLAN radio signal(beacon signal, etc.) in a WLAN channel and/or a WLAN frequency bandhaving a high priority. Further, the processor 160 activates a timer fortiming a period during which the WLAN scan should be continued, on thebasis of the period information. The processor 160 performs the WLANscan only at a timing at which the WLAN scan should be performed, on thebasis of the timing information. It is noted that when there is noperiod information, the processor 160 may scan only once (one shot scan)by using reception of the WLAN on request as a trigger.

It is noted that even when the processor 160 switches the WLANcommunication unit 112 to an on state in response to the WLAN onrequest, it is preferable for the processor 160 not to display theswitching on the user interface 120. This is to prevent a user fromrecognizing that an automatic

WLAN on is a malfunction, which is different from a case where a userperforms the operation to switch the WLAN communication unit 112 to anon state.

In step S808, the WLAN communication unit 112 of the UE 100 receives thebeacon signal from the AP 300. When the WLAN scan is performed in thecorresponding WLAN channel and timing, the processor 160 detects thebeacon signal from the AP 300 to discover the connectable AP 300.

In step S809, the processor 160 determines whether or not a timerindicating a period during which the WLAN scan should be continuedexpires. When the timer expires without the connectable AP 300 not beingdiscovered, the processor 160 switches the WLAN communication unit 112to an off state. Here, description is provided on the assumption thatthe connectable AP 300 is discovered during the timer running (stepS810).

In step S811, the processor 160 of the UE 100 transmits a connectionrequest to the AP 300, by the WLAN communication unit 112, to the AP300. As a result, the connection between the UE 100 and the AP 300 isestablished.

(Summary of Fifth Embodiment)

The eNB 200 according to the fifth embodiment transmits the WLAN onrequest to the UE 100. The WLAN on request includes the scan controlinformation for controlling the WLAN scan. After switching the WLANcommunication unit 112 to an on state in response to reception of theWLAN on request, the UE 100 controls the WLAN scan in accordance withthe scan control information included in the WLAN on request. Therefore,when the WLAN communication unit 112 is switched by the eNB 200 to an onstate, it is possible to establish a state where it is possible tooffload the eNB 200. Further, it is possible to efficiently perform theWLAN scan in accordance with the scan control information from the eNB200, and thus, the UE 100 is capable of reducing the power consumptionin the WLAN scan.

In the fifth embodiment, the eNB 200 acquires at least one of the UElocation information indicating the geographical location of the UE 100and the AP operation information indicating the operation status of theAP 300. Then, the eNB 200 controls to transmit the WLAN on request onthe basis of the acquired information. As a result, the eNB 200 iscapable of appropriately determining whether or not to transmit the WLANon request to the UE 100. Further, it is possible to appropriately set acontent of the scan control information to be included in the WLAN onrequest.

In the fifth embodiment, prior to reception of the WLAN on request, theUE 100 notifies the eNB 200 of at least one of the WLAN capabilityinformation indicating the WLAN communication capability of the UE 100and the WLAN off information indicating that the WLAN communication unit112 is in an off state. The eNB 200 controls to transmit the WLAN onrequest on the basis of the information received from the UE 100. As aresult, the eNB 200 is capable of appropriately determining whether ornot to transmit the WLAN on request to the UE 100.

In the fifth embodiment, the scan control information includes at leastone of the channel information for designating a WLAN channel subject tothe WLAN scan or a WLAN channel not subject to the WLAN scan, and thefrequency band information for designating a WLAN frequency band subjectto the WLAN scan or a WLAN frequency band not subject to the WLAN scan.As a result, the UE 100 is capable of limiting the WLAN channel and/orthe WLAN frequency band subject to the WLAN scan, and thus, it ispossible to reduce the power consumption in the WLAN scan.

In the fifth embodiment, the scan control information includes thepriority information for designating a WLAN channel and/or a WLANfrequency band where reception of the WLAN radio signal should bepreferentially attempted in the WLAN scan. As a result, in the WLANscan, the UE 100 is capable of discovering early the available WLANchannel, and thus, it is possible to reduce the power consumption in theWLAN scan.

In the fifth embodiment, the scan control information includes at leastone of the period information for designating a period during which theWLAN scan should be continued, and the timing information fordesignating a timing at which the WLAN scan should be performed. As aresult, the UE 100 is capable of limiting the period during which and/orthe timing at which the WLAN scan is performed, and thus, it is possibleto reduce the power consumption in the WLAN scan.

[First Modification of Fifth Embodiment]

Description is provided with a case where in the above-describedoperation sequence, the WLAN communication unit 112 of the UE 100 is inan off state, and the WLAN off information to that effect is notifiedfrom the UE 100 to the eNB 200. However, the eNB 200 may transmit theWLAN on request to the UE 100 irrespective of the WLAN off information.When the WLAN communication unit 112 is in an on state and the WLAN onrequest is received from the eNB 200, the processor 160 of the UE 100ignores the WLAN on request.

Further, description is provided with a case where in theabove-described operation sequence, the UE 100 supports the WLANcommunication and the WLAN capability information to that effect isnotified from the UE 100 to the eNB 200. However, the eNB 200 maytransmit the WLAN on request to the UE 100 irrespective of the WLANcapability information. The UE 100 that does not support the WLANcommunication ignores the WLAN on request even when the cellularcommunication unit 111 receives the WLAN on request from the eNB 200.

[Second Modification of Fifth Embodiment]

Prior to receiving the WLAN on request, the UE 100 may notify the eNB200 of information on the reception level of the GNSS signal. When thereception level of the GNSS signal is low, it is possible to estimatethat the UE 100 is located indoors, and otherwise, it is possible toestimate that the UE 100 is located outdoors. Further, there are someWLAN frequency bands that are prohibited from being used outdoors.Therefore, when it is possible to estimate that the UE 100 is locatedoutdoors, the eNB 200 preferably generates the WLAN frequency bandinformation so that a WLAN frequency band that is prohibited from beingused outdoors is not subject to the WLAN scan.

[Sixth Embodiment]

Next, a sixth embodiment will be described.

A case is assumed where the UE 100 is not connected to a cell managed bythe eNB 200 and performs data communication with the AP 300 in awireless LAN system. In this case, there is a problem that when the UE100 is off the coverage of the AP 300, data communication is interrupteduntil the UE 100 is connected to the cell of the eNB 200.

Therefore, an object of the sixth embodiment is to seamlessly transferfrom data communication in a wireless LAN system to data communicationin a cellular communication system.

(System Configuration)

FIG. 20 is a system configuration diagram according to the sixthembodiment.

As shown in FIG. 20, in the sixth embodiment, the E-UTRAN 10 includesthe eNB 200 (evolved Node-B) and a HeNB 400 (Home evolved Node-B). TheeNB 200 corresponds to a cellular base station.

The HeNB 400 manages a specific cell (small cell/femto cell) having anarrower cover range than a cell managed by the eNB 200 (large cell:macro cell) (see FIG. 22). The HeNB performs radio communication withthe UE that has established a connection (RRC connection) with thespecific cell.

The specific cell is called a “CSG cell”, a “hybrid cell”, or an “opencell” according to a set access mode.

The CSG cell is a cell accessible only by a UE 100 (called a “memberUE”) having an access right, and broadcasts a CSG ID. The UE 100 holds alist (whitelist) of a CSG ID of an CSG cell for which the UE 100 has anaccess right, and determines the presence or absence of access right onthe basis of the whitelist and the CSG ID broadcast by the CSG cell.

The hybrid cell is a cell in which the member UE is more advantageouslytreated as compared with the non-member UE, and broadcasts informationindicating that the hybrid cell is a cell released also to thenon-member UE, in addition to the CSG ID. The UE 100 determines thepresence or absence of access right on the basis of the whitelist andthe CSG ID broadcast by the hybrid cell.

The open cell is a cell in which the UE 100 is equivalently treatedregardless of whether the UE 100 is a member, and does not broadcast theCSG ID. In view of the UE 100, the open cell is equal to a cell.

It is noted that the MME/S-GW 500 verifies the UE 100 for access rightto the CSG cell.

Further, the HeNB 400 and the AP 300 are directly connected to eachother through an arbitrary interface of an operator. Therefore, the HeNB400 has data directly transferred from the AP 300.

The HeNB 400 and the AP 300 may be disposed in the same location(Collocated). That is, the HeNB 400 may be of collocated type. Forexample, as the HeNB 400 of collocated type, the HeNB 400 and the AP 300may be of integrated type in which the HeNB 400 and the AP 300 aredisposed in the same housing. In this case, the HeNB 400 and the AP 300may share a controller.

Next, the configuration of the HeNB 400 will be described.

FIG. 21 is a block diagram of the HeNB 400. As shown in FIG. 21, theHeNB 400 includes an antenna 401, a cellular communication unit 410, anetwork interface 420, a memory 430, and a processor 440. The memory 430and the processor 440 configure a controller. It is noted that thememory 430 is integrated with the processor 440, and this set (that is,a chipset) may be a processor configuring a controller.

The antenna 401 and the cellular communication unit 410 are used fortransmitting and receiving a cellular radio signal. The cellularcommunication unit 410 converts a baseband signal output from theprocessor 440 into the cellular radio signal, and transmits the samefrom the antenna 401. Further, the cellular communication unit 410converts the cellular radio signal received by the antenna 401 into thebaseband signal, and outputs the same to the processor 440. In thepresent embodiment, the cellular communication unit 410 forms a CSGcell.

The network interface 420 is connected to the neighboring eNB 200 or theneighboring HeNB 400 via the X2 interface and is connected to theMME/S-GW 500 via the Si interface. Further, the network interface 420 isconnected to the AP 300 via an interface that directly connects the AP300 and the HeNB 400 (hereinafter, “specific interface” whereappropriate). The specific interface is used for communication with theAP 300. For example, user data is transferred via the specific interfacefrom the AP 300.

The memory 430 stores a program to be executed by the processor 440 andinformation to be used for a process by the processor 440. The processor440 includes a baseband processor that performs modulation anddemodulation, encoding and decoding, etc., on the baseband signal and aCPU that performs various processes by executing the program stored inthe memory 430. The processor 440 executes various types of processesand various types of communication protocols described later.

It is noted that in the present embodiment, the network interface 320 inthe AP 300 is connected to the HeNB 400 via a specific interface thatdirectly connects the AP 300 and the HeNB 400. The specific interface inthe AP 300 is used for communication with the HeNB 400. For example,user data is transferred to the HeNB 400 via the specific interface.

(Collocated AP List)

In the present embodiment, the UE 100 has a collocated AP list. The UE100 and the eNB 200 share the collocated AP list.

The collocated AP list is of collocated type located at the same placeas the AP 300, and includes a cell ID of a small cell managed by theHeNB 400 of collocated type connected directly to the AP 300, andlocation information of the HeNB 400. The collocated AP list may includeinformation indicating an identifier of the AP 300 connected directly tothe HeNB 400.

The UE 100 acquires the collocated AP list from the eNB 200. Forexample, the UE 100 receives the collocated AP list from the eNB 200,during establishment of a connection, during execution of a handover, orat a timing at which a paging area is changed.

The eNB 200 may transmit the collocated AP list to the UE 100 on thebasis of capability information indicating that the UE 100 supportscommunication methods of both the cellular communication and the WLANcommunication.

(Operation According to Sixth Embodiment)

Next, an operation according to the sixth embodiment will be describedwith reference from FIG. 22 to FIG. 24. FIG. 22 is a diagram showing apositional relation among the UE 100, the eNB 200, the AP 300, and theHeNB 400 according to the sixth embodiment. FIG. 23 and FIG. 24 are asequence diagram for describing an operation according to the sixthembodiment.

As shown in FIG. 22, the UE 100 exists in a large cell managed by theeNB 200. Further, the HeNB 400 and the AP 300 are disposed in the samelocation, and the HeNB 400 and the AP 300 are directly connected.Specifically, the AP 300 is an AP (collocated-type AP) integrated withthe HeNB 400.

A coverage of a small cell managed by the HeNB 400 and a coverage of theAP 300 at least partially overlap. In the present embodiment, thecoverage of the AP 300 and the coverage of the small cell are the same,or the coverage of the AP 300 is larger than the coverage of the smallcell. Further, the coverage of the small cell and the coverage of the AP300 are contained in the coverage of the large cell.

Further, in the present embodiment, description proceeds with anassumption that the UE 100 moves in a direction leaving the HeNB 400 tobe off the coverage of the small cell. Further, description proceedswith an assumption that the UE 100 has an access right to the HeNB 400.That is, the UE is a CSG member, and the small cell is a hybrid cell oran open cell.

As shown in FIG. 23, the UE 100 recognizes that the UE 100 is beingconnected to the AP 300 and the connected AP 300 is an AP 300 integratedwith the HeNB 400. For example, when receiving from the AP 300 that theAP 300 is of integrated type or receiving broadcast information from theHeNB 400 that the AP 300 is of integrated type, the UE 100 recognizesthat the AP 300 is of integrated type. Alternatively, the UE 100 mayrecognize that the connected AP 300 is an integrated-type AP 300 on thebasis of the collocated AP list. Specifically, the UE 100 recognizesthat the connected AP 300 is the integrated-type AP 300 when anidentifier of the connected AP 300 and an identifier of the AP 300included in the collocated AP list match.

Further, as shown in FIG. 23, the UE 100 receives a reference signalfrom the HeNB 400 and a reference signal from the eNB 200. The UE 100measures a signal intensity of each reference signal. Further, the UE100 is connected to the AP 300 (Offloading) and in an idle state (IDLE).That is, the UE 100 is not connected to the eNB 200 and the HeNB 400.

As shown in FIG. 23, in step S901, the UE 100 detects deterioration ofthe signal intensity of the reference signal from the HeNB 400.

The UE 100 moves in a direction leaving the HeNB 400, and thus, thesignal intensity of the reference signal gradually weakens. The UE 100detects the deterioration of the signal intensity when the signalintensity of the reference signal from the HeNB 400 becomes less than apredetermined value that is a value by which it is possible to ensurethe communication quality. As a result, the UE 100 determines on thebasis of the deterioration of the signal intensity from the HeNB 400that the connection with the AP 300 becomes difficult.

It is noted that in the present embodiment, the AP 300 is an APintegrated with the HeNB 400, and thus, when the signal intensity of thereference signal from the HeNB 400 weakens, it is possible to estimatethat the UE 100 comes close to the coverage end of the AP 300, as aresult of which even when the signal intensity of the beacon signal fromthe AP 300 is equal to or more than a predetermined value that is avalue by which it is possible to ensure the communication quality, theUE 100 determines that the connection with the AP 300 becomes difficultwhen the signal intensity from the HeNB 400 is less than a predeterminedvalue that is a value by which the connection with the AP 300 becomesdifficult.

It is noted that the UE 100 exists in the large cell, and thus, thesignal intensity from the eNB 200 is equal to or more than apredetermined value by which it is possible to ensure the communicationquality.

In step S902, the UE 100 makes an RRC connection request including atransfer request, to the eNB 200. The eNB 200 receives the RRCconnection request.

The transfer request is a request to transfer user data about the UE 100owned by the AP 300 connected to the UE 100, via the HeNB 400 to the eNB200.

In step S903, the eNB 200 transmits ACK/NACK that responds to the RRCconnection request, to the UE 100. The UE 100 receives the ACK/NACK thatresponds to the RRC connection request.

In the present embodiment, description proceeds with an assumption thatthe eNB 200 transmits the ACK (acknowledgment) to the UE 100.

In step S904, Connection Procedure is performed.

In step S905, the UE 100 transmits, to the eNB 200, a Connectioncomplete message indicating that the Connection Procedure is completed.

In the present embodiment, in the Connection complete message,information on a transfer cancellation timer is included.

The transfer cancellation timer is used for canceling a process oftransferring user data from the AP 300 to the eNB 200. When the transfercancellation timer expires, the eNB 200 cancels the process oftransferring the user data from the AP 300 to the eNB 200.

In step S906, each of the UE 100 and the eNB 200 activates the transfercancellation timer.

In step S907, the eNB 200 transmits, to the HeNB 400, a messageconfirming whether or not the HeNB 400 is capable of transferring theuser data. Specifically, the eNB 200 performs a Buffer borrowing requestto request temporary borrowing of a buffer of the HeNB 400 to transferthe user data. The HeNB 400 receives the Buffer borrowing request.

In step S908, the HeNB 400 transmits ACK/NACK that responds to theBuffer borrowing request, to the eNB 200.

It is noted that the HeNB 400 may transmit the ACK to the eNB 200 evenwhen the UE 100 does not have the access right to the HeNB 400. Further,even when the UE 100 is not a CSG member (that is, the UE 100 does nothave the access right to the HeNB 400), the HeNB 400 may determinewhether to accept the transfer request of the eNB 200 only whenreceiving the Buffer borrowing request. Alternatively, the transferrequest may be accepted only to the transfer request of the eNB 200 towhich the ACK that responds to the Buffer borrowing request istransmitted after receiving the Buffer borrowing request.

Further, the HeNB 400 transmits the NACK (negative acknowledgment) whena buffer capacity is equal to or more than a predetermined value andthere is not a sufficient free space. Further, the HeNB 400 may transmitthe NACK (negative acknowledgment) when the UE 100 does not have theaccess right to the HeNB 400.

In the present embodiment, description proceeds with an assumption thatthe HeNB 400 transmits the ACK (acknowledgment) to the eNB 200. It isnoted that a case where the HeNB 400 transmits the NACK (negativeacknowledgment) to the eNB 200 will be described later.

In step S909, the eNB 200 makes a transfer request (Forwarding Request)to the HeNB 400. The HeNB 400 receives the transfer request.

In step S910, on the basis of the transfer request from the eNB 200, theHeNB 400 makes a transfer request (Forwarding Request) to transfer theuser data of the UE 100 to the AP 300.

It is noted that in the present embodiment, the UE 100 is a CSG member,and thus, it is possible to use a resource of the HeNB 400. Generally,the UE 100 which is not a CSG member is not capable of using theresource of the HeNB 400. However, even for the UE 100 which is not aCSG member, the HeNB 400 may make, on the basis of the transfer requestfrom the eNB 200, a transfer request to transfer the user data of the UE100 to the AP 300.

In step S911, the AP 300 transfers, to the HeNB 400, the user data ofthe UE 100 on the basis of the transfer request from the HeNB 400. Here,the AP 300 is directly connected to the HeNB 400 via a specificinterface, and thus, the transfer from the AP 300 to the HeNB 400 israpidly performed.

In step S912, the HeNB 400 transfers, to the eNB 200, the user datatransferred from the AP 300. Specifically, the HeNB 400 transfers theuser data to the eNB 200 via the X2 interface. As a result, the userdata is transferred from the AP 300 by way of the HeNB 400 to the eNB200.

In step S913, the UE 100 and the eNB 200 use the transferred user datato perform data communication.

When the UE 100 is connected with the AP 300, the connection with the AP300 may be ended.

Next, a case where the HeNB 400 transmits the NACK (negativeacknowledgment) to the eNB 200 will be described by using FIG. 24.

Steps S1001 to S1008 in FIG. 24 correspond to steps S901 to S908 in FIG.23.

As shown in FIG. 24, in step S1009, the eNB 200 determines whether theNACK is received in response to the Buffer borrowing request. When theACK is received, the eNB 200 performs a process in step S909 in FIG. 23.

On the other hand, when the NACK is received, in step S1010, in responseto the transfer request from the UE 100, the eNB 200 transmits aresponse (NACK) indicating that the user data is not transferred fromthe AP 300. The UE 100 receives the response (NACK) of the transferrequest.

In step S1011, when receiving the response (NACK) of the transferrequest, the UE 100 increments a transfer failure counter (Forwardingtrial Counter), by one, provided in the UE 100.

In step S1012, the UE 100 determines whether or not to perform onceagain step S1002 (that is, whether or not to perform the transferrequest in step S902. When the UE 100 determines to perform the transferrequest (in a case of Yes), the UE 100 makes once again the transferrequest to the eNB 200. For example, when the transfer failure counterdoes not reach a predetermined value, the UE 100 makes once again thetransfer request to the eNB 200. Therefore, the UE 100 repeats thetransfer request to the eNB 200 until the transfer failure counterreaches a predetermined value. The eNB 200 that has received thetransfer request starts a process in step S1007 (that is, step S907). Itis noted that when information on a transfer cancellation timer isincluded in the transfer request, the eNB 200 starts a process in stepS1006 (that is, step S906). When the transfer cancellation timer isbeing activated, the eNB 200 resets the activated transfer cancellationtimer, and activates the transfer cancellation timer on the basis of theinformation on the transfer cancellation timer.

On the other hand, when the transfer failure counter reaches apredetermined value, the UE 100 determines to not make the transferrequest. In this case, the UE 100 performs a process as usual. Forexample, the UE 100 may transmit the RRC connection request to the eNB200 or/and the HeNB 400 by reselection. In this case, the UE 100 maytransmit the RRC connection request while being connected to the AP 300.

[Summary of Sixth Embodiment]

In the present embodiment, when it is determined that the connectionbetween the UE 100 and the AP 300 directly connected to the HeNB 400becomes difficult, the UE 100 is connected to the eNB 200, and the AP300 transfers the user data of the UE 100 by way of the HeNB 400 to theeNB 200. As a result, the AP 300 is capable of transferring the userdata to the HeNB 400 via a specific interface, and thus, the eNB 200 iscapable of rapidly acquiring the user data of the UE 100 owned by the AP300. This restrains stoppage of a user data flow, resulting in aseamless data communication.

In the present embodiment, when determining that the connection with theAP 300 becomes difficult and that it is possible to connect with a largecell, the UE 100 makes the RRC connection request and the transferrequest for transferring the user data owned by the AP 300 to the eNB200, to the eNB 200. Further, the AP 300 transfers the user data to theeNB 200, resulting from the transfer request from the UE 100. Thus, theUE 100, which determines by itself that the connection with the AP 300becomes difficult, is capable of making an appropriate determination onthe basis of an actual radio situation of the UE 100, resulting in aseamless data communication.

In the present embodiment, when the UE 100 is of collocated type inwhich the AP 300 is located at the same place as the HeNB 400, even whenthe signal intensity of the beacon signal from the AP 300 is equal to ormore than a predetermined value that is a value by which it is possibleto ensure the communication quality, if the signal intensity from theHeNB 400 is less than a predetermined value that is a value by which itis possible to ensure the communication quality, then it may be possibleto determine that the connection with the AP 300 becomes difficult.Thus, the AP 300 is of collocated type, and therefore, when the signalintensity from the HeNB 400 is less than a predetermined value, it ispossible to estimate that the UE 100 exists near the coverage of the AP300, and as a result, when the transfer request is made in advance, aseamless data communication is further enabled.

In the present embodiment, the eNB 200 transmits the transfer request tothe HeNB 400 when receiving the transfer request from the UE 100, theHeNB 400 transmits the transfer request to the AP 300 when receiving thetransfer request from the eNB 200, and the AP 300 transfers the userdata by way of the HeNB 400 to the eNB 200 when receiving the transferrequest from the HeNB 400. Thus, the HeNB 400 and the AP 300 aredirectly connected, and therefore, the eNB 200 is capable of morerapidly making the transfer request than making the transfer request byway of the core network, to the AP 300. As a result, it is possible tofurther enable a seamless data communication.

In the present embodiment, even when the UE 100 is not a CSG member, theHeNB 400 transfers the user data transferred from the AP 300, to the eNB200. As a result, even when the UE 100 is not a CSG member, the eNB 200is capable of rapidly acquiring the user data of the UE 100 owned by theAP 300, and thus, it is possible to further enable a seamless datacommunication.

In the present embodiment, when receiving the NACK from the eNB 200 thatresponds to the transfer request from the UE 100, the UE 100 makes thetransfer request once again. As a consequence, even if the transferrequest is not accepted first, when a buffer capacity of the HeNB 400 isreduced as a result of the transfer request being made once again bymaking the transfer request once again, the transfer request isaccepted, and thus, a seamless data communication is enabled.

In the present embodiment, the UE 100 repeatedly makes the transferrequest until the number of times that NACK is received reaches apredetermined value. Thus, the UE 100 is capable of performing aseamless data communication when the transfer request is accepted as aresult of the transfer request being repeated. On the other hand, whenthe transfer request is not accepted even when the transfer request issent a predetermined number of times, the UE 100 is capable ofrestraining a meaningless transfer request transmission by canceling thetransfer request.

[Seventh Embodiment]

(Operation According to Seventh Embodiment)

Next, an operation according to a seventh embodiment will be describedby using FIG. 25 and FIG. 26. FIG. 25 is a diagram showing a positionalrelation among the UE 100, the eNB 200, the HeNB 400, and the AP 300according to the seventh embodiment. FIG. 26 is a sequence diagram fordescribing an operation according to the seventh embodiment.

It is noted that a description will be provided while focusing on aportion different from the above-described embodiment, and a descriptionof a similar portion will be omitted.

It is noted that in the seventh embodiment, in much the same way as inthe sixth embodiment, the UE 100 recognizes that the UE 100 is beingconnected to the AP 300 and the connected AP 300 is an AP 300 integratedwith the HeNB 400.

In the above-described sixth embodiment, the coverage of the AP 300 islarger than the coverage of the small cell. In the present embodiment,the coverage of the AP 300 and the coverage of the small cell are thesame, or as shown in FIG. 25, the coverage of the small cell is largerthan the coverage of the AP 300.

As shown in FIG. 26, in step S1101, the UE 100 detects deterioration ofthe signal intensity of the beacon signal from the AP 300.

The UE 100 moves in a direction leaving the HeNB 400, and thus, thesignal intensity of the beacon signal gradually weakens. The UE 100detects the deterioration of the signal intensity when the signalintensity of the beacon signal from the AP 300 becomes less than apredetermined value. As a result, the UE 100 determines on the basis ofthe deterioration of the signal intensity from the AP 300 that theconnection with the AP 300 becomes difficult. In the present embodiment,the UE 100 determines that the connection with the AP 300 becomesdifficult when the signal intensity of the beacon signal from the AP 300becomes less than a predetermined value before the signal intensityreceived from the HeNB 400 becomes less than a predetermined value thatis a value by which it is possible to ensure the communication quality.

It is noted that the UE 100 exists in the small cell, and thus, thesignal intensity from the HeNB 400 is equal to or more than apredetermined value.

In step S1102, the UE 100 makes an RRC connection request including atransfer request, to the HeNB 400. The HeNB 400 receives the RRCconnection request.

When the signal intensity of the reference signal from the HeNB 400 isequal to or more than a predetermined value, the UE 100 makes theconnection request to the HeNB 400.

It is noted that when the signal intensity of the reference signal fromthe HeNB 400 is less than a predetermined value, the UE 100 makes theconnection request to the eNB 200.

In step S1103, the HeNB 400 transmits ACK/NACK that responds to the RRCconnection request, to the UE 100. The UE 100 receives the ACK/NACK thatresponds to the RRC connection request.

In the present embodiment, description proceeds with an assumption thatthe HeNB 400 transmits the ACK (acknowledgment) to the UE 100.

In step S1104, Connection Procedure is performed.

In step S1105, the HeNB 400 transmits, to the AP 300, the transferrequest to transfer the user data from the AP 300 to the HeNB 400, onthe basis of the transfer request from the UE 100. The AP 300 receivesthe transfer request.

In step S1106, the AP 300 transfers the user data to the HeNB 400.

In step S1107, the HeNB 400 transmits a handover request (H.O. RequestAck) to the eNB 200 when the user data is transferred. The eNB 200receives the handover request.

When receiving the measurement report indicating that the signalintensity from the HeNB 400 received by the UE 100 is less than apredetermined value, the HeNB 400 may transmit the handover request tothe eNB 200.

Further, when the UE 100 is not a CSG member, the HeNB 400 is notcapable of using the resource (a resources for control signals and abuffer of the HeNB 400) of the HeNB 400, for the UE which is not a CSGmember.

However, when the UE 100 is not a CSG member, the HeNB 400 may permitthe UE 100 to use the resources of the HeNB 400 on condition that thehandover request is immediately transmitted to the eNB 200 when the userdata is transferred to the HeNB 400 and when the CSG cell of the HeNB400 and the UE 100 are connected.

In step S1108, a handover request response (H. O. Request Response) thatresponds to the handover request is transmitted to the HeNB 400.

In step S1109, a handover procedure (H. O. Procedure) is performed.

In step S1110, the UE 100 and the eNB 200 use the transferred user datato perform data communication.

(Summary of Seventh Embodiment)

In the present embodiment, when determining that the connection with theAP 300 becomes difficult and that it is possible to connect with a smallcell, the UE 100 makes to the HeNB 400 the RRC connection request andthe transfer request for transferring the user data owned by the AP 300to the HeNB 400. Further, the AP 300 transfers the user data to the HeNB400, on the basis of the transfer request from the UE 100. As a result,the HeNB 400 is capable of rapidly acquiring the user data of the UE 100owned by the AP 300, and thus, it is possible to restrain a flow of theuser data from stopping and possible to further enable a seamless datacommunication.

In the present embodiment, the UE 100 determines that the connectionwith the AP 300 becomes difficult when the signal intensity of thebeacon signal from the AP 300 becomes less than a predetermined valuebefore the signal intensity received from the HeNB 400 becomes less thana predetermined value that is a value by which it is possible to ensurethe communication quality. As a result, the UE 100 is capable ofappropriately selecting the HeNB 400 as a target to which the transferrequest is sent.

In the present embodiment, when the UE 100 is not a CSG member, the HeNB400 may immediately transmit the handover request to the eNB 200 whenthe user data is transferred and when the CSG cell of the HeNB 400 andthe UE 100 are connected. As a result, even the UE 100 which is not aCSG member is capable of a seamless data communication by using the HeNB400.

[Other Embodiments]

In the operation sequences according to the above-described first andsecond embodiments, the operation performed by the eNB 200 (basestation) may be performed by another network device such as an upperdevice (for example, RNC) of the eNB 200 instead of the eNB 200.

In the above-described third embodiment and fourth embodiments, noconsideration is given to the operation environment where a movable AP(such as a mobile router) exists in the transport T. However, it ispossible to apply the present invention to such an operationenvironment. For example, when being connected to the AP (movable AP) bythe WLAN communication unit 112 and detecting that the UE movement speedrapidly decreases, the processor 160 of the UE 100 may restrict a startof connection with another AP (AP 300) while maintaining the connectionwith that AP (movable AP).

In the modification of the third embodiment and the modification of thefourth embodiment, an example is described where the AP blacklist isprovided from the eNB 200. However, the UE 100 may previously hold theAP blacklist.

In the above-described fifth embodiment, the information transmitted andreceived between the UE 100 and the eNB 200 may be an

RRC message or information element thereof.

In the above-described fifth embodiment, a case is assumed where the eNB200 is a macro cell base station having a broad coverage; however, theeNB 200 may be a small cell base station having a coverage comparable tothat of the AP 300. Further, when the eNB 200 is a small cell basestation and the AP 300 is collocated with the eNB 200, it may bepossible to omit the determination (step S805) whether or not the UE 100comes close to the AP 300.

The second modification of the above-described fifth embodiment may beapplied to a process closed by the UE 100. Specifically, when it ispossible to estimate on the basis of the reception level of the GNSSsignal that the UE 100 is located outdoors, the UE 100 regards the WLANfrequency band prohibited to be used outdoors not subject to the WLANscan.

In the above-described sixth and seventh embodiments, the UE 100determines whether or not the connection between the UE 100 and the AP300 becomes difficult; however this is not limiting. The AP 300 maydetermine whether or not the connection between the UE 100 and the AP300 becomes difficult.

Specifically, when the AP 300 measures the signal intensity receivedfrom the UE 100 and the signal intensity received from the UE 100 isless than a predetermined value that is a value by which it is possibleto ensure the communication quality, the AP 300 determines that theconnection between the UE 100 and the AP 300 becomes difficult.

When the AP 300 determines that the connection between the UE 100 andthe AP 300 becomes difficult, the user data is transferred based on (A)the initiative of the UE or (B) the initiative of the AP 300, as shownbelow.

(A) the Initiative of the UE 100

When determining that the connection between the UE 100 and the AP 300becomes difficult, the AP 300 notifies the UE 100 that the connectionbetween the UE 100 and the AP 300 becomes difficult. When receiving thenotification, the UE 100 measures the signal intensity of each referencesignal of the eNB 200 and the HeNB 400.

The UE 100 makes the RRC connection request including the transferrequest to the eNB 200 or the HeNB 400 having a signal intensity beingequal to or more than a predetermined value, out of the referencesignals of the eNB 200 and the HeNB 400. The processes after this areperformed in much the same way as in the sixth or seventh embodiment.

When such a process is performed, the UE 100 does not need to perform adetermination process that the connection between the UE 100 and the AP300 becomes difficult, and thus, it is possible to restrain a processload in the UE 100.

(B) the Initiative of the AP 300

When the AP 300 determines that the connection between the UE 100 andthe AP 300 becomes difficult, the AP 300 makes a request the eNB 200 orthe HeNB 400 adjacent to the AP 300 so that the eNB 200 or the HeNB 400adjacent to the AP 300 is connected to the UE 100. When making theconnection request to the eNB 200, the AP 300 requests the eNB 200 byway of the HeNB 400. Description proceeds with an assumption that the AP300 requests the HeNB 400 to be connected to the UE 100, below.

When receiving the connection request from the AP 300, the HeNB 400transmits, by paging, for example, to the UE 100 a notificationindicating that the HeNB 400 is connected to the UE 100. The UE 100 isconnected to the HeNB 400 on the basis of the notification.

When the connection with the UE 100 is completed, the HeNB 400 transmitsa connection complete notification to the AP 300. When receiving theconnection complete notification, the AP 300 starts transferring theuser data to the HeNB 400.

It is noted that when making the connection request to the eNB 200, theAP 300 receives the connection complete notification from the eNB 200 tothe AP 300 by way of the HeNB 400.

When such a process is performed, it is possible to restrain a processload of the UE 100 because the UE 100 does not need to transmit thetransfer request.

It is noted that when the connection with the eNB 200 or the HeNB 400 iscompleted, the UE 100 may perform a process for ending the connectionbetween the UE 100 and the AP 300.

Further, in the above-described sixth and seventh embodiments, whendetermining that the connection with the AP 300 becomes difficult, theUE 100 is connected to the HeNB 400 directly connected to the AP 300with which the UE 100 is connected or the eNB 200 that manages the largecell enveloping the coverage of the AP; this is not limiting. Forexample, the UE 100 may be connected to the HeNB 400 adjacent to theHeNB 400 directly connected to the AP 300 with which the UE 100 isconnected. In this case, the HeNB 400 directly connected to the AP 300with which the UE 100 is connected transfers the user data to theadjacent HeNB 400 via the X2 interface.

Further, in the above-described sixth and seventh embodiments, thecoverage of the small cell and the coverage of the AP 300 are envelopedin the coverage of the large cell; however, this is not limiting. Thecoverage of the small cell and the coverage of the AP 300 may partiallyoverlap the coverage of the large cell.

Further, in the above-described sixth and seventh embodiments, as thesmall cell base station, the HeNB 400 is described as an example;however, this is not limiting. For example, a small cell base stationmay be a femto cell or a pico cell that manages the small cell.

Further, in the above-described sixth embodiment, the eNB 200 makes theBuffer borrowing request; however, this is not limiting. The eNB 200 maymake the transfer request to the HeNB 400 without making the Bufferborrowing request.

It is noted that when the reference signal from the HeNB 400 and thebeacon signal from the AP 300 are less than a predetermined value at thesame time, or when the beacon signal from the AP 300 is less than apredetermined value before a predetermined time passes since thereference signal from the HeNB 400 is less than a predetermined value,the UE 100 may make the RRC connection request including the transferrequest to the eNB 200.

It is noted that in the above-described sixth and seventh embodiments,the UE 100 is in an idle state; however, when the UE 100 is in a stateof being connected to the HeNB 400, the UE 100 implements a normalhandover to the eNB 200.

In addition, in each above-described embodiment, the LTE system isdescribed as one example of the cellular communication system; however,this is not limited to the LTE system, and the present invention may beapplied to a cellular communication system other than the LTE system.

In addition, the entire content of Japanese Patent Application No.2013-100600 (filed on May 10, 2013), Japanese Patent Application No.2013-100777 (filed on May 10, 2013), Japanese Patent Application No.2013-100779 (filed on May 10, 2013), Japanese Patent Application No.2013-100780 (filed on May 10, 2013), and U.S. Provisional ApplicationNo. 61/864,250 (filed on Aug. 9, 2013) is incorporated in the presentspecification by reference.

INDUSTRIAL APPLICABILITY

As described above, the communication control method and the userterminal according to the present invention is useful for a mobilecommunication field.

The invention claimed is:
 1. A communication control method forperforming offload to transfer a traffic load of an Evolved UniversalTerrestrial Radio Access Network (E-UTRAN) to a Wireless Local AreaNetwork (WLAN), comprising: starting the offload by the user terminal;determining, by the user terminal, whether the offload is canceled afterstarting the offload, on a basis of a communication status in the WLAN;and receiving, by the user terminal, configuration information from theE-UTRAN before releasing a connection between the user terminal and theE-UTRAN, wherein the configuration information is information for aconfiguration of an operation of the user terminal after starting theoffload and after releasing the connection, and the communicationcontrol method further comprises: starting use of the configurationinformation by the user terminal only after transition to an idle state.2. The communication control method according to claim 1, furthercomprising: canceling the offload and discarding the configurationinformation, by the user terminal, in response to determining that theoffload is canceled.
 3. A user terminal, comprising: a controllerconfigured to start offload to transfer a traffic of an EvolvedUniversal Terrestrial Radio Access Network (E-UTRAN) to a Wireless LocalArea Network (WLAN), wherein the controller is further configured to:determine whether the offload is canceled after starting the offload, ona basis of a communication status in the WLAN; and receive configurationinformation from the E-UTRAN before releasing a connection between theuser terminal and the E-UTRAN, wherein the configuration information isinformation for a configuration of an operation of the user terminalafter starting the offload and after releasing the connection, and thecontroller is further configured to: start use of the configurationinformation by the user terminal only after transition to an idle state.4. The user terminal according to claim 3, wherein the controller isfurther configured to cancel the offload and discard the configurationinformation in response to determining that the offload is canceled. 5.A processor to be provided in a user terminal, the processorcommunicatively coupled to memory including instructions that whenexecuted by the processor, cause the processor to: start offload totransfer a traffic of an Evolved Universal Terrestrial Radio AccessNetwork (E-UTRAN) to a Wireless Local Area Network (WLAN); determinewhether the offload is canceled after starting the offload, on a basisof a communication status in the WLAN; and receive configurationinformation from the E-UTRAN before releasing a connection between theuser terminal and the E-UTRAN, wherein the configuration information isinformation for a configuration of an operation of the user terminalafter starting the offload and after releasing the connection, and theinstructions cause the processor to start use of the configurationinformation by the user terminal only after transition to an idle state.6. The processor according to claim 5, wherein the instructions causethe processor to cancel the offload and discard the configurationinformation in response to determining that the offload is canceled. 7.The communication control method according to claim 1, furthercomprising: transmitting, by the user terminal, a notification to theE-UTRAN, wherein the notification indicates keeping a connection withthe WLAN.
 8. The user terminal according to claim 3, wherein thecontroller is further configured to transmit a notification to theE-UTRAN, and the notification indicates keeping a connection with theWLAN.
 9. The processor according to claim 5, wherein the instructionscause the processor to transmit a notification to the E-UTRAN, and thenotification indicates keeping a connection with the WLAN.